Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Revision IB2 Topic 1
Document related concepts
Chemical equilibrium wikipedia , lookup
Metastable inner-shell molecular state wikipedia , lookup
Chemistry: A Volatile History wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
Atomic orbital wikipedia , lookup
Electronegativity wikipedia , lookup
Chemical thermodynamics wikipedia , lookup
Atomic nucleus wikipedia , lookup
Biochemistry wikipedia , lookup
Bent's rule wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Resonance (chemistry) wikipedia , lookup
History of molecular theory wikipedia , lookup
Electrochemistry wikipedia , lookup
Light-dependent reactions wikipedia , lookup
Photoredox catalysis wikipedia , lookup
Electrolysis of water wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Chemical reaction wikipedia , lookup
Marcus theory wikipedia , lookup
Metallic bonding wikipedia , lookup
Electron configuration wikipedia , lookup
Click chemistry wikipedia , lookup
Molecular orbital diagram wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
Metalloprotein wikipedia , lookup
George S. Hammond wikipedia , lookup
Rate equation wikipedia , lookup
Chemical bond wikipedia , lookup
Physical organic chemistry wikipedia , lookup
Hypervalent molecule wikipedia , lookup
Strychnine total synthesis wikipedia , lookup
Stoichiometry wikipedia , lookup
Transition state theory wikipedia , lookup
Atomic theory wikipedia , lookup
Transcript
Revision IB2 1. 2. 3. Topic 1 How many oxygen atoms are present in 0.0500 mol carbon dioxide? 22 A. 3.01 × 10 B. 6.02 × 10 C. 6.02 × 10 D. 1.20 × 10 22 23 24 Which solution contains the greatest amount (in mol) of solute? 3 –3 3 –3 3 –3 3 –3 A. 10.0 cm of 0.500 mol dm NaCl B. 20.0 cm of 0.400 mol dm NaCl C. 30.0 cm of 0.300 mol dm NaCl D. 40.0 cm of 0.200 mol dm NaCl The equation for the complete combustion of butane is 2C4H10 + 13O2 → 8CO2 + 10H2O What is the amount (in mol) of carbon dioxide formed by the complete combustion of three moles of butane? A. B. C. D. 4. 4 8 12 24 The reaction of ethanal and oxygen can be represented by the unbalanced equation below. __ CH3CHO + __ O2 → __ CO2 + __ H2O When the equation is balanced using the smallest possible integers, what is the coefficient for O2? A. B. C. D. 5. Which is a correct definition of the term empirical formula? A. B. C. D. 6. 3 4 5 6 formula showing the numbers of atoms present in a compound formula showing the numbers of elements present in a compound formula showing the actual numbers of atoms of each element in a compound formula showing the simplest ratio of numbers of atoms of each element in a compound −3 What volume of 0.500 mol dm HCl(aq) is required to react completely with 10.0 g of calcium carbonate according to the equation below? CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g) 7. A. 100 cm B. 200 cm C. 300 cm D. 400 cm 3 3 3 3 6.0 moles of Fe2O3(s) reacts with 9.0 moles of carbon in a blast furnace according to the equation below. Fe2O3(s) + 3C(s) → 2Fe(s) + 3CO(g) What is the limiting reagent and hence the theoretical yield of iron? Limiting reagent Fe2O3 Fe2O3 carbon carbon A. B. C. D. 8. Theoretical yield of iron 6.0 mol 12.0 mol 9.0 mol 6.0 mol Consider the following equation. 2C4H10(g) + 1302(g) → 8CO2(g) + 10H2O(1) How many moles of CO2(g) are produced by the complete combustion of 58 g of butane, C4H10 (g)? A. B. C. D. 9. 4 8 12 16 Assuming complete reaction, what volume of 0.200 mol dm 3 –3 25 0 cm of 0.200 mol dm Ba(OH)2(aq)? A. 12.5 cm B. 25.0 cm C. 50.0 cm D. 75.0 cm 3 3 3 3 –3 HCl(aq) is required to neutralize 10. Consider the equation below. Fe(s) + S(s) → FeS(s) If 10.0 g of iron is heated with 10.0 g of sulfur to form iron(II) sulfide, what is the theoretical yield of FeS in grams? A. B. C. D 11. 10.0 + 10.0 87.91 × 10.0 55.85 87.91 × 10.0 32.06 55.85 × 10.0 32.06 Which of the following compounds has/have the empirical formula CH2O? I. II. III. A. B. C. D. 12. 1 g of CH3Cl 1 g of CH2Cl2 1 g of CHCl3 1 g of CCl4 3 What amount of NaCl (in moles) is required to prepare 250 cm of a 0.200 mol dm A. B. C. D. 14. II only III only I and II only II and III only Which of the following contains the greatest number of molecules? A. B. C. D. 13. CH3COOH C6H12O6 C12H22O11 50.0 1.25 0.800 0.0500 What is the coefficient for O2 (g) when the equation below is balanced? __C3H8(g) + __O2(g) → __CO2(g) + __H2O(g) A. B. C. D. 2 3 5 7 −3 solution? 15. The percentage by mass of the elements in a compound is C = 72%, H = 12 %, O = 16%. What is the mole ratio of C : H in the empirical formula of this compound? A. B. C. D. 16. 17. 18. 1:1 1:2 1:6 6:1 How many hydrogen atoms are contained in one mole of ethanol, C2H5OH? A. B. 5 6 C. 1.0 × 10 D. 3.6 × 10 23 24 + Which solution contains the smallest amount of H ions? 3 –3 A. 10.0 cm of 0.250 mol dm HCl B. 20.0 cm of 0.250 mol dm 3 –3 3 –3 HCl D. 10.0 cm of 0.500 mol dm HCl C. 10.0 cm3 of 0.250 mol dm –3 H2SO4 Lithium hydroxide reacts with carbon dioxide as follows. 2LiOH + CO2 → Li2 CO3 +H2O What mass (in grams) of lithium hydroxide is needed to react with 11 g of carbon dioxide? A. B. C. D. 19. 6 12 24 48 Copper can react with nitric acid as follows. 3Cu +_HNO3 → _Cu(NO3)2 +_H2O + _NO What is the coefficient for HNO3 when the equation is balanced? A. B. C. D. 4 6 8 10 20. The percentage composition by mass of a hydrocarbon is C = 85.6 % and H = 14.4 %. (a) Calculate the empirical formula of the hydrocarbon. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) A 1.00 g sample of the hydrocarbon at a temperature of 273 K and a pressure of 5 3 1.01 × 10 Pa(1.00 atm) has a volume of 0.399 dm . (i) Calculate the molar mass of the hydrocarbon. .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... .......................................................................................................................... (2) (ii) Deduce the molecular formula of the hydrocarbon. (1) (Total 5 marks) 21. 27.82 g of hydrated sodium carbonate crystals, Na2CO3. xH2O, was dissolved in water and 3 3 3 made up to 1.000 dm . 25.00 cm of this solution was neutralized by 48.80 cm of hydrochloric −3 acid of concentration 0.1000 mol dm . (a) Write an equation for the reaction between sodium carbonate and hydrochloric acid. ..................................................................................................................................... (2) (b) Calculate the molar concentration of the sodium carbonate solution neutralized by the hydrochloric acid. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (c) Determine the mass of sodium carbonate neutralized by the hydrochloric acid and hence 3 the mass of sodium carbonate present in the1.000dm of solution. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (d) Calculate the mass of water in the hydrated crystals and hence find the value of x. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (Total 12 marks) 22. An oxide of copper was reduced in a stream of hydrogen as shown below. excess hydrogen burning hydrogen gas oxide of copper in a dish HEAT After heating, the stream of hydrogen gas was maintained until the apparatus had cooled. The following results were obtained. Mass of empty dish = 13.80 g Mass of dish and contents before heating = 21.75 g Mass of dish and contents after heating and leaving to cool = 20.15 g (a) Explain why the stream of hydrogen gas was maintained until the apparatus cooled. ..................................................................................................................................... ..................................................................................................................................... (1) (b) Calculate the empirical formula of the oxide of copper using the data above, assuming complete reduction of the oxide. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (c) Write an equation for the reaction that occurred. ..................................................................................................................................... (1) (d) State two changes that would be observed inside the tube as it was heated. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 7 marks) (a) 23. Write an equation for the formation of zinc iodide from zinc and iodine. ..................................................................................................................................... (1) (b) 100.0 g of zinc is allowed to react with 100.0 g of iodine producing zinc iodide. Calculate the amount (in moles) of zinc and iodine, and hence determine which reactant is in excess. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (c) Calculate the mass of zinc iodide that will be produced. ..................................................................................................................................... ..................................................................................................................................... (1) (Total 5 marks) 24. 3 3 100 cm of ethene, C2H4, is burned in 400 cm of oxygen, producing carbon dioxide and some liquid water. Some oxygen remains unreacted. (a) Write the equation for the complete combustion of ethene. ..................................................................................................................................... (2) (b) Calculate the volume of carbon dioxide produced and the volume of oxygen remaining. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 4 marks) (i) 25. Calcium carbonate is added to separate solutions of hydrochloric acid and ethanoic acid of the same concentration. State one similarity and one difference in the observations you could make. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. (2) (ii) Write an equation for the reaction between hydrochloric acid and calcium carbonate. ………………………………………………………………………………………….. ………………………………………………………………………………………….. (2) –3 (iii) Determine the volume of 1.50 mol dm of hydrochloric acid that would react with exactly 1.25 g of calcium carbonate. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. (3) (iv) Calculate the volume of carbon dioxide, measured at 273 K and 5 1.01 × 10 Pa, which would be produced when 1.25 g of calcium carbonate reacts completely with the hydrochloric acid. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. ………………………………………………………………………………………….. (2) (Total 9 marks) 1. 2. 3. 4. 5. 6. 7. B C C C D D D 8. 9. 10. 11. 12. 13. 14. A C B C A D C 15. 16. 17. 18. 19. B D A B C 85.6 14.4 (a) 20. mole ratio C : H = 12.01 : 1.01 = 7.13 :14.3; No penalty for using integer atomic masses. empirical formula is CH 2 ; (b) (i) 2 number of moles of gas n = 1.01 × 10 2 kPa (.399 dm 3 ); PV = mass ; ; RT molar mass 8.314 J (273 K) mol K 1.00 g –1 .017 mol = 56.3 (g mol ) 2 OR mass of molar me the volu 22.4 dm molar mass is the 3at STP; 1.00 × 22.4 –1 = 56.1 (g mol ) 0.399 (ii) Accept answers in range 56.0 to 56.3. Accept two, three or four significant figures. C 4H8; 1 No ECF. [5] (a) 21. (b) Na2CO3 + 2HCl → 2NaCl + H2O + CO2 Award [1] for correct products, [1] for correct balancing. State symbols not required. Accept correct equation with hydrated salt. Accept ionic equation and partial neutralisation. n(Na2CO3) = 1 2 2 n(HCl); 48.80 n(HCl) = 1000 × 0.1000 = 0.00 488 mol; (1000 ) = .00024 × −3 concentration of Na2CO3 25 = 0.0976 mol dm ; Award [3] for correct answer. Award [3] for correct answer based on equation in (a), i.e. allow ECF from (a). Note –1(SF) is possible. (c) 3 Mr Na2CO3 = 2(22.99) + 12.01 + 3(16.00) = 105.99; Accept 106. mass of Na2CO3 reacting with HCl(aq) = 0.00244 × 105.99 = 0.259 g; Allow ECF from (b) and M. 1000 3 mass of Na2CO3 in 1.000 dm = 0.259 × 25 = 10.36 g; Note –1(U) is possible. 3 (d) mass of water in crystals = (27.82 −10.36) = 17.46 g; Allow ECF from (b) and (c). 17.46 number of moles of water = 18.02 = 0.9689; Accept 0.97 mole ratio Na2CO3 : H2O = 0.0976 : 0.9689; x = 10; 4 [12] (a) 22. (b) to prevent (re)oxidation of the copper / OWTTE; 1.60 number of moles of oxygen 16.00 = 0.10; number of moles of copper = 6.35 63.55 =0.10; empirical formula = Cu (0.10) : O (0.10) = CuO; Allow ECF. Award [1] for CuO with no working. Alternate solution 6.35 7.95 = 79.8 % 70.8 63.5 = 1.25 (c) (d) 1 3 1.60 7.95 = 20.2 % 20.2 16 = 1.29 H2 + CuO → Cu + H2O; Allow ECF. (black copper oxide) solid turns red / brown; condensation / water vapour (on sides of test tube); Accept change colour. Do not accept reduction of sample size. 1 2 [7] (a) 23. (b) Zn + I2 → ZnI2; Accept equilibrium sign. – 1 65.37 gmol g (moles of) iodine =100.0 = 0.3940; – 1 253.8 gmol 1 g= 1.530; (moles of) zinc =100.0 3 ECF throughout. –1 (SF) possible. (reacting ratio is 1:1, therefore) zinc is in excess; Must be consistent with calculation above. (c) (amount of zinc iodide = amount of iodine used = 100.0 moles) 253.8 100 . 0 (mass of zinc iodide = × (65.37 + 253.8) = 253.8) 125.8 (g); 253.8 1 Use ECF throughout. -1 (SF) possible. [5] (a) 24. (b) C2H4 + 3O2 → 2CO2 + 2H2O; Award [1] for formulas and [1] for coefficients. 3 (CO2 produced) = 200 (cm ) ; 3 (O2 remaining) = 100 (cm ) ; ECF from 2(a). 2 2 [4] 25. (ii) (i) bubbling / effervescence / dissolving of / gas given off CaCO3 (do not accept CO2 produced); more vigorous reaction with HCl / OWTTE; 2HCl(aq) + CaCO3(s) → CaCl2(aq) + CO2(g) + H2O(1); [1] for correct formulas, [1] for balanced, state symbols not essential. 2 2 1.25 (iii) (iv) amount of CaCO3 = 100.09 (no penalty for use of 100); amount of HCl = 2 × 0.0125 = 0.0250 mol (allow ECF); 3 3 volume of HCl = 0.0167 dm / 16.7 cm (allow ECF); 1:1 ratio of CaCO3 to CO2 to / use 0.0125 moles CO2 (allow ECF); 3 3 –4 3 (0.0125 × 22.4) = 0.28 dm / 280 cm / 2.8 × 10 m (allow ECF); Accept calculation using pV=nRT. 3 1 [9] IB2 Revision 1. The electron arrangement of sodium is 2.8.1. How many occupied main electron energy levels are there in an atom of sodium? A. B. C. D. 2. B. C. D. 10 12 14 22 16 + O 16 2+ O 18 2+ O 16 18 + ( O O) 69 71 69.2 69.8 70.0 70.2 What is the difference between two neutral atoms represented by the symbols A. B. C. D. 6. 2+ Mg ion? A certain sample of element Z contains 60% of Z and 40% of Z. What is the relative atomic mass of element Z in this sample? A. B. C. D. 5. 24 12 Which ion would undergo the greatest deflection in a mass spectrometer? A. 4. 1 3 10 11 How many electrons are there in one A. B. C. D. 3. Topic 2 59 27 Co and 59 28 Ni ? The number of neutrons only. The number of protons and electrons only. The number of protons and neutrons only. The number of protons, neutrons and electrons. 69 71 A certain sample of element Z contains 60% of Z and 40% of Z. What is the relative atomic mass of element Z in this sample? A. B. C. D. 69.2 69.8 70.0 70.2 7. 26 A. B. C. D. 8. Protons 10 12 12 14 Neutrons 14 14 26 12 Electrons 12 10 10 12 How many valence electrons are present in an atom of an element with atomic number 16? A. B. C. D. 9. 2+ How many protons, neutrons and electrons are there in the species Mg ? 2 4 6 8 Electrons are directed into an electric field from left to right as indicated by the arrow in the diagram below. Which path is most probable for these electrons? 1 + 2 4 – 3 A. B. C. D. 10. What is the correct sequence for the processes occurring in a mass spectrometer? A. B. C. D. 11. 1 2 3 4 vaporization, ionization, acceleration, deflection vaporization, acceleration, ionization, deflection ionization, vaporization, acceleration, deflection ionization, vaporization, deflection, acceleration Which statement is correct for the emission spectrum of the hydrogen atom? A. B. C. D. The lines converge at lower energies. The lines are produced when electrons move from lower to higher energy levels. The lines in the visible region involve electron transitions into the energy level closest to the nucleus. The line corresponding to the greatest emission of energy is in the ultraviolet region. 12. 19 – What is the correct number of each particle in a fluoride ion, F ? protons 9 9 9 9 A. B. C. D. 13. electrons 8 9 10 10 How many electrons are there in all the d orbitals in an atom of xenon? A. B. C. D. 14. neutrons 10 10 10 19 10 18 20 36 What is the total number of p orbitals containing one or more electrons in germanium (atomic number 32)? A. B. C. D. 2 3 5 8 15 15. State the number of protons, electrons and neutrons in the ion 7 3− N . …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (Total 2 marks) 16. (a) Evidence for the existence of energy levels in atoms is provided by line spectra. State how a line spectrum differs from a continuous spectrum. ..................................................................................................................................... ..................................................................................................................................... (1) (b) On the diagram below draw four lines in the visible line spectrum of hydrogen. (1) Low energy High energy (c) Explain how the formation of lines indicates the presence of energy levels. ..................................................................................................................................... ..................................................................................................................................... (1) (Total 3 marks) 17. (a) Define the term isotope. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) 69 71 A sample of gallium exists as two isotopes, Ga, relative abundance 61.2 %, and Ga, relative abundance 38.8 %. Calculate the relative atomic mass of gallium. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (1) (Total 3 marks) 18. (a) Define the term isotope. (2) (b) A sample of argon exists as a mixture of three isotopes. mass number 36, relative abundance 0.337 % mass number 38, relative abundance 0.0630 % mass number 40, relative abundance 99.6 % Calculate the relative atomic mass of argon. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (c) 56 3+ State the number of electrons, protons and neutrons in the ion Fe . electrons: ............................. protons: ............................. neutrons: ........................... (2) (Total 6 marks) 19. (a) State a physical property that is different for isotopes of an element. ..................................................................................................................................... (1) (b) 35 37 Chlorine exists as two isotopes, Cl and Cl. The relative atomic mass of chlorineis 35.45. Calculate the percentage abundance of each isotope. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 3 marks) 20. (i) State the full electron configuration for argon. …………………………………………………………………………………………… (1) (ii) Give the formulas of two oppositely charged ions which have the same electron configuration as argon. …………………………………………………………………………………………… (2) (Total 3 marks) 1. 2. 3. 4. 5. B A B B D 15. 7 protons, 8 neutrons, 10 electrons; Award [2] for three correct and [1] for two correct. 6. 7. 8. 9. 10. B B C A A 11. 12. 13. 14. D C C D 2 [2] 16. (b) (c) (a) continuous spectrum has all colours / wavelengths / frequencies whereas line spectrum has only (lines of) sharp / discrete / specific colours / wavelengths / frequencies; lines get closer together towards high energy; line represents electron transitions between energy levels / OWTTE; (a) atoms of the same element / same atomic number / same number of protons; different numbers of neutrons / mass numbers; Award only [1] max if reference made to elements but not atoms. 17. (b) 1 1 1 [3] 2 (69 × 61.2 71 + 38.8) relative atomic mass = 100 = 69.8; 1 –1 (SF) possible (treat 69 and 71 as integers) [3] (a) atoms of the same element / same number of protons / same atomic number; having different numbers of neutrons / different (mass number); Award only [1] max if reference made to elements but not atoms. 18. 2 36 × 0.337 + 38 × 0.0630 + 40 × 99.6 ; 100 (b) relative atomic mass = (c) 23 electrons; 26 protons; 30 neutrons; 2 Award [2] for three correct, [1] for two correct. 2 [6] (a) mass / density / for gases: rate of effusion or diffusion / melting point / boiling point 1 Do not accept mass number. 19. (b) 35 if Cl = x, then (x = 35.00) + (1 – x) 37.00 = 35.45 Award [1] for set up. therefore, x = 0.775; 35 37 Cl = 77.5 % and Cl = 22.5 %; (need both for mark); 2 [3] (i) 20. 2 2 6 2 6 1s 2s 2p 3s 3p ;. 1 2 (ii) 6 Do not accept [Ne] 3s 3p or 2, 8, 8. + 2+ 3+ 4+ K / Ca / Sc / Ti ; – 2– 3– Cl / S / P ; Accept other suitable pairs of ions. 2 [3] IB2 Revision 1. Which two elements react most vigorously with each other? A. B. C. D. 2. 5. the number of occupied electron energy levels the number of neutrons in the most common isotope the number of electrons in the atom the atomic mass When the following species are arranged in order of increasing radius, what is the correct order? – + A. Cl , Ar, K B. K , Ar , Cl C. Cl , K , Ar D. Ar, Cl , K + – – + – + Rubidium is an element in the same group of the periodic table as lithium and sodium. It is likely to be a metal which has a A. B. C. D. 6. atomic radius electronegativity ionic radius melting point What increases in equal steps of one from left to right in the periodic table for the elements lithium to neon? A. B. C. D. 4. chlorine and lithium chlorine and potassium iodine and lithium iodine and potassium Which property decreases down group 7 in the periodic table? A. B. C. D. 3. Topic 3 high melting point and reacts slowly with water. high melting point and reacts vigorously with water. low melting point and reacts vigorously with water. low melting point and reacts slowly with water. Which of the reactions below occur as written? A. B. C. D. – – I. Br2 + 2I → 2Br + I2 II. Br2 + 2Cl → 2Br + Cl2 – – I only II only Both I and II Neither I nor II PAGE \*Arabic 32 7. Which of the following oxides is (are) gas(es) at room temperature? I. II. III. A. B. C. D. 8. I only II only I and II only II and III only Which of the physical properties below decrease with increasing atomic number for both the alkali metals and the halogens? I. II. III. A. B. C. D. 9. I only II only III only I and III only Li Be B Mg Which general trends are correct for the oxides of the period 3 elements (Na2O to Cl2O)? I. II. III. A. B. C. D. 11. Atomic radius Ionization energy Melting point For which element are the group number and the period number the same? A. B. C. D. 10. SiO2 P4O6 SO2 Acid character decreases. Electrical conductivity (in the molten state) decreases. Bonding changes from ionic to covalent. I and II only I and III only II and III only I, II and III Which properties of period 3 elements increase from sodium to argon? I. II. III. A. B. C. D. Nuclear charge Atomic radius Electronegativity I and II only I and III only II and III only I, II and III PAGE \*Arabic 32 12. Which is an essential feature of a ligand? A. B. C. D. 13. a negative charge an odd number of electrons the presence of two or more atoms the presence of a non-bonding pair of electrons Explain the following features of the melting points of the period 3 elements. Refer to bonding and structure, and use information from Table 6 in the Data Booklet. (i) The difference between the values for sodium and magnesium ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (ii) The high value for silicon ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (iii) The difference between the values for chlorine and argon ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 7 marks) PAGE \*Arabic 32 14. For the elements of period 3 (Na to Ar), state and explain (i) the general trend in ionization energy ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (ii) any exceptions to the general trend. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (Total 6 marks) 15. (a) Classify each of the following oxides as acidic, basic or amphoteric. (i) aluminium oxide …………………………………………………………………………………… (1) (ii) sodium oxide …………………………………………………………………………………… (1) (iii) sulfur dioxide …………………………………………………………………………………… (1) PAGE \*Arabic 32 (b) Write an equation for each reaction between water and (i) sodium oxide …………………………………………………………………………………… …………………………………………………………………………………… (1) (ii) sulfur dioxide. …………………………………………………………………………………… …………………………………………………………………………………… (1) (Total 5 marks) 16. (i) Describe three similarities and one difference in the reactions of lithium and potassium with water. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) (ii) Give an equation for one of these reactions. Suggest a pH value for the resulting solution, and give a reason for your answer. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) (Total 7 marks) PAGE \*Arabic 32 17. State and explain the trends in the atomic radius and the ionization energy (i) for the alkali metals Li to Cs. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) (ii) for the period 3 elements Na to Cl. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) (Total 8 marks) 18. Table 8 of the Data Booklet gives the atomic and ionic radii of elements. State and explain the difference between (i) the atomic radius of nitrogen and oxygen. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) PAGE \*Arabic 32 (ii) the atomic radius of nitrogen and phosphorus. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (iii) the atomic and ionic radius of nitrogen. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) (Total 5 marks) 19. Nitrogen is found in period 2 and group 5 of the periodic table. (i) Distinguish between the terms period and group. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (ii) State the electron arrangement of nitrogen and explain why it is found in period 2 and group 5 of the periodic table. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) (Total 4 marks) PAGE \*Arabic 32 20. Two characteristics of the d-block (transition) elements are that they exhibit variable oxidation states and form coloured compounds. (i) State two possible oxidation states for iron and explain these in terms of electron arrangements. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (ii) Explain why many compounds of d-block (transition) elements are coloured. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 5 marks) 21. By reference to the structure and bonding in the compounds NaCl and SiCl4 (i) state and explain the differences in conductivity in the liquid state. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) PAGE \*Arabic 32 (ii) predict an approximate pH value for a solution formed by adding each compound separately to water. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (Total 7 marks) 22. Elements with atomic number 21 to 30 are d-block elements. (a) Identify which of these elements are not considered to be typical transition elements. ..................................................................................................................................... ..................................................................................................................................... (1) (b) Complex ions consist of a central metal ion surrounded by ligands. Define the term ligand. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (c) Complete the table below to show the oxidation state of the transition element. (3) ion 2– Cr2O7 2− [CuCl4] 3+ [Fe(H2O)6] oxidation state PAGE \*Arabic 32 (d) Identify two transition elements used as catalysts in industrial processes, stating the process in each case. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (e) Apart from the formation of complex ions and apart from their use as catalysts, state two other properties of transition elements. ..................................................................................................................................... ..................................................................................................................................... (2) (Total 10 marks) 23. 2+ Define the term ligand. Cu (aq) reacts with ammonia to form the complex ion 2+ [Cu(NH3)4] . Explain this reaction in terms of an acid-base theory, and outline the bonding in 2+ the complex ion formed between Cu and NH3. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ (Total 4 marks) PAGE \*Arabic 32 24. Outline the reasoning for the following in terms of electronic configuration: (i) The first ionization energy of Al is lower than that of Mg. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (ii) 3+ 2+ V (aq) is coloured and can behave as a reducing agent, whereas Zn (aq) is not coloured and does not behave as a reducing agent. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (6) (Total 8 marks) PAGE \*Arabic 32 1. 2. 3. 4. B B C B 13. (ii) (iii) 5. 6. 7. 8. C A B B 9. 10. 11. 12. (i) metallic bonding in Na and Mg; more delocalized (OWTTE) electrons in Mg / Mg ion is smaller /more positive; stronger attraction in Mg between positive ions and delocalized electrons; 3 Si is macromolecular / a giant molecule / OWTTE; many (covalent) bonds to be broken; A clear implication of covalent bonding must be made if both marks are to be awarded. van der Waals’ / weak intermolecular forces / London dispersion forces; Cl2 has more electrons / higher Mr than Ar; B C B D 2 2 [7] 14. (ii) (a) (i) ionization energy increases; nuclear charge increases / electron is closer to the nucleus / atomic radius decreases; Al is lower than expected; S is lower than expected; Al – electron removed is in p sub-level / at higher energy than in Mg; S – electron removed is in an orbital that contains a second electron that repels it / change to half-filled p subshell; Award [1] if Al and S given without any extra detail. 2 4 [6] 15. (ii) (iii) (b) (ii) (a) (i) aluminium oxide amphoteric; sodium oxide basic; sulfur dioxide acidic; 3 + − (i) Na2O + H2O → 2Na + 2OH ; SO2 + H2O → H2SO3; + – + Accept NaOH and H + HSO3 / 2H + SO 2 2− 3 . [5] 16. (ii) (i) similarities [3 max] the metal floats / moves on the surface; fizzing / effervescence / bubbles; (accept sound is produced) solution gets hot; solution becomes alkaline / basic; they react to form the metal hydroxide; hydrogen is evolved; differences [1 max] flame / hydrogen burns with potassium (and not with lithium) / reaction faster / more vigorous with potassium / slower or less vigorous with lithium; + – + + – 2Li + 2H2O → 2Li + 2OH + H2 / 2K + 2H2O → 2K + 2OH + H2; Accept LiOH / KOH. pH ≥ 11; 4 max − LiOH/KOH is a strong base/strong alkali / high concentration of OH ; 3 [7] PAGE \*Arabic 32 17. (ii) (i) Li to Cs atomic radius increases; because more full energy levels are used or occupied / outer electrons further from nucleus / outer electrons in a higher shell; ionization energy decreases; because the electron removed is further from the nucleus / increased repulsion by inner-shell electrons; Accept increased shielding effect. Na to Cl atomic radius decreases; because nuclear charge increases and electrons are added to same main (outer) energy level; ionization energy increases; because nuclear charge increases and the electron removed is closer to the nucleus/is in the same energy level; Accept “core charge” for “nuclear charge”. In (i) and (ii) explanation mark dependent on correct trend. 4 4 [8] 18. (ii) (iii) (i) atomic radius of N > O because O has greater nuclear charge; greater attraction for the outer electrons / OWTTE; atomic radius of P > N because P has outer electrons in an energy level further from the nucleus / OWTTE; 3− 3− N >N / ionic radius > atomic radius because N has more electrons than protons; so the electrons are held less tightly / OWTTE; 3− Award [1] for greater repulsion in N due to more electrons (no reference to protons). 2 1 2 [5] 19. (ii) (i) period is a horizontal row in the periodic table and a group is a vertical column / OWTTE; 2,5; electrons in two energy levels / shells; five outer / valence electrons; 1 3 [4] (i) 20. (ii) +2 and +3 / Fe 2+ and Fe 3+ ; 2+ both s electrons are lost giving Fe and one more d electron is 3+ also lost to form Fe ; presence of unpaired electrons; the d orbitals are split into two energy levels; electrons move between these energy levels; electrons can absorb energy from light of visible wavelength / OWTTE; 3 Award [1] each for any three. 2 [5] 21. (ii) (i) NaCl conducts and SiCl4 does not; NaCl ionic and SiCl4 covalent; ions can move in liquid (in NaCl) / OWTTE; NaCl pH = 7; + − salt of strong acid and strong base / Na and Cl not hydrolysed; SiCl4 pH = 0 to 3; HCl is formed / strong acid formed; 3 4 [7] PAGE \*Arabic 15 (a) 22. (b) scandium and zinc / Sc and Zn; Both needed for the mark. Accept copper/Cu if given in addition to Sc and Zn i.e. all three needed for the mark. species / neutral molecules / anions which contain a non-bonding pair of electrons; able to form coordinate/dative covalent bonds; 1 2 (c) ion 2− 2− 3+ Cr2O7 2[CuCl4] [Fe(H2O)6] oxidation state +6 +2 +3 Accept 6+, 2+, 3+. If given as 6, 2, 3 or (VI), (II), (III), Award [2] only. (d) (e) V / V2O5 in the contact process; Fe in the Haber process; Ni in the conversion of alkenes to alkanes / hydrogenation reactions; Award [1] each for any two. Accept any other suitable examples. variable oxidation states; coloured compounds; Accept any other suitable examples. 3 2 max 2 [10] 23. ligand: a molecule or ion that can bond to a (central) metal ion (to form a complex); 2+ NH3: Lewis base and Cu : Lewis acid (need both for mark); 2+ each NH3 / ligand donates an electron pair (to Cu ); forming coordinate covalent / dative covalent bond; 4 [4] 24. (ii) 2 2 1 (i) Mg: 3s and Al: 3s 3p (need both for mark); 3p electron is higher in energy than 3s (and easier to remove); 3+ 3 2+ 10 V : [Ar]3d and Zn : [Ar] 3d (need both for mark); colour due to splitting of partially filled d orbitals (at different energy levels); electronic transitions between these are responsible for colour; 3+ 2+ V has partially filled d orbitals / Zn does not; 3+ V not in its highest oxidation state (and can be oxidized); 2+ Zn in its highest oxidation state (and cannot be further oxidized); 6 2 [8] PAGE \*Arabic 15 IB2 Revision 1. Which statement best describes the attraction present in metallic bonding? A. B. C. D. 2. The elements are metals. The elements are non-metals. The elements have very low electronegativity values. The elements have very different electronegativity values. What happens when sodium and oxygen combine together? A. B. C. D. 6. only hydrogen bonds covalent bonds and hydrogen bonds covalent bonds and van der Waals’ forces hydrogen bonds and van der Waals’ forces Which statement is correct about two elements whose atoms form a covalent bond with each other? A. B. C. D. 5. Cu(s) Hg(l) H2(g) LiOH(aq) In ethanol, C2H5OH (l), there are covalent bonds, hydrogen bonds and van der Waals’ forces. Which bonds or forces are broken when ethanol is vaporized? A. B. C. D. 4. the attraction between nuclei and electrons the attraction between positive ions and electrons the attraction between positive ions and negative ions the attraction between protons and electrons Which substance has the lowest electrical conductivity? A. B. C. D. 3. Topic 4 Each sodium atom gains one electron. Each sodium atom loses one electron. Each oxygen atom gains one electron. Each oxygen atom loses one electron. Consider the following statements. 2– I. All carbon-oxygen bond lengths are equal in CO II. All carbon-oxygen bond lengths are equal in CH3COOH. III. All carbon-oxygen bond lengths are equal in CH3COO . 3 . − Which statements are correct? A. B. C. D. I and II only I and III only II and III only I, II and III PAGE \*Arabic 15 7. Which molecule is non-polar? A. B. C. D. 8. Why is the boiling point of PH3 lower than that of NH3? A. B. C. D. 9. lone pair-lone pair > lone pair-bond pair > bond pair-bond pair. bond pair-bond pair > lone pair-bond pair > lone pair-lone pair. lone pair-lone pair > bond pair-bond pair > bond pair-lone pair. bond pair-bond pair > lone pair-lone pair > lone pair-bond pair. Which of the following species is (are) planar (has (have) all the atoms in one plane)? A. B. C. D. 12. SO2 CO2 H2S Cl2O According to VSEPR theory, repulsion between electron pairs in a valence shell decreases in the order A. B. C. D. 11. PH3 is non-polar whereas NH3 is polar. PH3 is not hydrogen bonded whereas NH3 is hydrogen bonded. Van der Waals’ forces are weaker in PH3 than in NH3 The molar mass of PH3 is greater than that of NH3 Which molecule is linear? A. B. C. D. 10. H2CO SO3 NF3 CHCl3 I. CO 23– II. NO 3– III. SO 2– 3 I only II only I and II only II and III only −3 Which substance is most soluble in water (in mol dm ) at 298 K? A. B. C. D. CH3CH3 CH3OCH3 CH3CH2OH CH3CH2CH2CH2OH PAGE \*Arabic 15 13. 14. What is the Lewis (electron dot) structure for sulfur dioxide? A. O S O B. O S O C. O S D. O S O Based on electronegativity values, which bond is the most polar? A. B. C. D. 15. X3Y X2Y XY2 XY Which statements are correct about diamond, graphite and a C60 fullerene? A. B. C. D. 17. B–C C–O N–O O–F What is the formula of an ionic compound formed by element X (group 2) and element Y (group 6)? A. B. C. D. 16. O I. The poorest electrical conductor of the three is diamond. II. III. The atoms in graphite and C60 fullerene are sp hybridized. The atoms in diamond and C60 fullerene are arranged in hexagons. 2 I and II only I and III only II and III only I, II and III Which statement is correct about multiple bonding between carbon atoms? A. B. C. D. Double bonds are formed by two π bonds. Double bonds are weaker than single bonds. π bonds are formed by overlap between s orbitals. π bonds are weaker than sigma bonds. PAGE \*Arabic 15 18. – NO 3 is trigonal planar and NH3 is trigonal pyramidal. What is the type of hybridization of N in each of these species? – N in NO 3 19. 21. 2 A. sp B. sp C. Sp D. sp 3 sp 2 2 sp 3 2 sp 3 3 sp Which statement about sigma and pi bonds is correct? A. B. C. D. 20. N in NH3 Sigma bonds are formed only by s orbitals and pi bonds are formed only by p orbitals. Sigma bonds are formed only by p orbitals and pi bonds are formed only by s orbitals. Sigma bonds are formed by either s or p orbitals, pi bonds are formed only by p orbitals. Sigma and pi bonds are formed by either s or p orbitals. What is the molecular shape and the hybridization of the nitrogen atom in NH3? Molecular shape tetrahedral Hybridization A. B. trigonal planar sp C. trigonal pyramidal sp D. trigonal pyramidal sp (i) 3 sp 2 2 3 Use the VSEPR theory to predict and explain the shape and the bond angle of each of the molecules SCl2 and C2Cl2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (6) PAGE \*Arabic 15 (ii) Deduce whether or not each molecule is polar, giving a reason for your answer. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) (Total 9 marks) 22. Outline the principles of the valence shell electron pair repulsion (VSEPR) theory. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (Total 3 marks) 23. State the type of bonding in the compound SiCl4. Draw the Lewis structure for this compound. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (Total 3 marks) PAGE \*Arabic 15 24. The letters W, X, Y and Z represent four consecutive elements in the periodic table. The number of electrons in the highest occupied energy levels are: W: 3, X: 4, Y: 5, Z: 6 Write the formula for (i) an ionic compound formed from W and Y, showing the charges. …………………………………………………………………………………………… …………………………………………………………………………………………… (2) (ii) a covalent compound containing X and Z. …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (Total 3 marks) 25. Three scientists shared the Chemistry Nobel Prize in 1996 for the discovery of fullerenes. Fullerenes, like diamond and graphite, are allotropes of the element carbon. (i) State the structures of and the bonding in diamond and graphite. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) (ii) Compare and explain the hardness and electrical conductivity of diamond and graphite. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) PAGE \*Arabic 15 (iii) Predict and explain how the hardness and electrical conductivity of C60 fullerene would compare with that of diamond and graphite. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) (Total 10 marks) 26. (a) An important compound of nitrogen is ammonia, NH3. The chemistry of ammonia is influenced by its polarity and its ability to form hydrogen bonds. Polarity can be explained in terms of electronegativity. (i) Explain the term electronegativity. …………………………………………………………………………………… …………………………………………………………………………………… (2) (ii) Draw a diagram to show hydrogen bonding between two molecules of NH3. The diagram should include any dipoles and/or lone pairs of electrons …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (3) (iii) State the H–N–H bond angle in an ammonia molecule. ……………………………………………………………………………………… (1) PAGE \*Arabic 15 (iv) Explain why the ammonia molecule is polar. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (1) (b) + Ammonia reacts with hydrogen ions forming ammonium ions, NH4 . (i) State the H–N–H bond angle in an ammonium ion. …………………………………………………………………………………… (1) (ii) Explain why the H–N–H bond angle of NH3 is different from the H–N–H bond + angle of NH 4 ; referring to both species in your answer. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (3) (Total 11 marks) 27. (i) List the following substances in order of increasing boiling point (lowest first). CH3CHO C2H6 CH3COOH C2H5OH ……………………………………………………………………………………………… (2) PAGE \*Arabic 15 (ii) State whether each compound is polar or non-polar, and explain the order of boiling points in (c)(i). ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… (8) (Total 10 marks) 28. Draw Lewis (electron dot) structures for the following ions. – NO2 + NO2 Determine and explain the shape of each ion. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… (Total 6 marks) PAGE \*Arabic 15 29. Identify the strongest type of intermolecular force in each of the following compounds. CH3Cl ................................................................................................................................... CH4 ....................................................................................................................................... CH3OH ................................................................................................................................. (Total 3 marks) 30. (i) Draw Lewis (electron dot) structures for CO2 and H2S showing all valence electrons. (2) (ii) State the shape of each molecule and explain your answer in terms of VSEPR theory. CO2 ............................................................................................................................. ..................................................................................................................................... ..................................................................................................................................... H2S ............................................................................................................................. ..................................................................................................................................... ..................................................................................................................................... (4) (iii) State and explain whether each molecule is polar or non-polar. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 8 marks) 31. (i) Explain the meaning of the term hybridization. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (1) PAGE \*Arabic 15 (ii) Discuss the bonding in the molecule CH3CHCH2 with reference to the formation of σ and π bonds the length and strength of the carbon-carbon bonds the types of hybridization shown by the carbon atoms ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (6) (Total 7 marks) 32. For the following compounds PCl3 , PCl5 , POCl3 (i) Draw a Lewis structure for each molecule in the gas phase. (Show all non-bonding electron pairs.) (3) PAGE \*Arabic 15 (ii) State the shape of each molecule and predict the bond angles. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (6) (iii) Deduce whether or not each molecule is polar, giving a reason for your answer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 12 marks) 33. Atomic orbitals can mix by hybridization to form new orbitals for bonding. Identify the type of hybridization present in each of the three following molecules. Deduce and explain their shapes. (i) OF2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) PAGE \*Arabic 15 (ii) H2CO …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) (iii) C2H2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) (Total 9 marks) 34. In 1954 Linus Pauling was awarded the Chemistry Nobel Prize for his work on the nature of the chemical bond. Covalent bonds are one example of intramolecular bonding. Explain the formation of the following. (i) σ bonding …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) (ii) π bonding …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) PAGE \*Arabic 15 (iii) double bonds …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (iv) triple bonds …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (Total 6 marks) PAGE \*Arabic 15 1. 2. 3. 4. 5. 6. 7. B C D B B B B 8. 9. 10. 11. 12. 13. 14. B B A C C D B 15. 16. 17. 18. 19. 20. D A D A C D (i) SCl2 two bonding pairs, two non-bonding pairs; angular / bent / non-linear / V-shaped; Both these marks can be scored from a diagram. 90° < angle < 107°; C2Cl2 two charge centres around each C; linear; Both these marks can be scored from a diagram. angle = 180°; 6 21. (ii) SCl2 is polar; C2Cl2 is non-polar; No net dipole movement for C2Cl2 but angular SCl2 has a resultant dipole OWTTE; Mark can be scored from a diagram. Allow ECF based on the answers given to (i). 3 [9] 22. find number of electron pairs/charge centres in (valence shell of) central atom; electron pairs/charge centres (in valence shell) of central atom repel each other; to positions of minimum energy/repulsion / maximum stability; pairs forming a double or triple bond act as a single bond; non-bonding pairs repel more than bonding pairs / OWTTE; Do not accept repulsion between bonds or atoms. Award [1] each for any three points. 3 max [3] 23. Si—Cl bonds are covalent; 3 Cl Cl Si Cl Cl Accept lines for electron pairs. Award [1] for covalent bonds and [1] for lone pairs. [3] (i) 24. (ii) W XZ2; 3+ 3− Y Award [1] for formula (WY) and [1] for charges (W:3+Y:3-) 1 Answers must be in terms of X and Z. 2 [3] 25. (i) Diamond Graphite giant molecular / macromolecular / 3-D covalent bonds only; covalent bonds and van der Waals’ forces layer structure ; Award [1] for both shape and bonding in each case. Accept suitable diagrams. 2 (ii) Diamond poor / non-conductor no delocalized electrons hard rigid structure Award [1] per row. Graphite good conductor delocalized electrons soft layers can slide 4 PAGE \*Arabic 15 (iii) softer than diamond / harder than graphite; as C60 molecules can move over each other; conducts better than diamond / worse than graphite; as C60 has less delocalisation (of the unpaired bonding electrons) than graphite; 4 [10] (a) 26. (i) (relative) measure of an atom’s attraction for electrons; in a bond; 2 (ii) – + xx hydrogen bonding H N + +H H xx – + H N + +H (iii) (iv) (b) (ii) H Suitable diagram indicating dipoles; lone pairs of electrons; hydrogen bonding; 3 107°; 1 Accept answer in range 107 to 109° . molecule is asymmetrical / OWTTE; 1 (i) 1 109.5°; + NH4 has four bonding pairs (around central atom so is a regular tetrahedron); NH3 has three bonding pairs (of electrons) and one non-bonding pair; non-bonding pairs (of electrons) exert a greater repulsive force; Accept suitable diagrams. 3 [11] (i) 27. (ii) C2H6 < CH3CHO, < C2H5OH < CH3COOH; Award [2] if all correct, [1] if first and last correct. C 2H6 non polar; CH3CHO polar; C2H5OH polar; CH3COOH polar; Award [2] for all four correct, [1] for 3 or 2 correct. boiling point depends on intermolecular forces; least energy required for van der Waals’ forces / maximum energy for hydrogen bonding; C2H6 van der Waals’ forces only; CH3CHO dipole-dipole; C2H5OH and CH3COOH hydrogen bonding; hydrogen bonding is stronger in CH3COOH / greater polarity / greater molecular mass / greater van der Waals’ forces; 2 8 [10] 50 28. x x x x NO2 O x x x x x x N x O x O x x x x ; x x x + x Nx Ox ; x Accept lines for pairs of electrons. If charge is missing, penalize only once. shape explanation ion NO2 x – + bent / angular; three charge centres one of which is a lone / non-bonding pair / OWTTE; linear; two charges centres / OWTTE; 6 [6] 29. CH3Cl – dipole-dipole attractions; CH4 – van der Waals’ / dispersion / London forces; CH3OH – hydrogen bond; 3 [3] 30. (i) O C O ; 2 H S H; Accept dots, crosses, a combination of dots and crosses or a line to represent a pair of electrons. (ii) (iii) CO2 is linear; two charge centres or bonds and no lone pairs (around C); HS is bent / v-shaped / angular; two bond pairs, two lone pairs (around S); CO2 is non-polar, H2S is polar; bond polarities cancel CO2 but not in H2S; 4 2 [8] 31. (i) (ii) combining of atomic orbitals to form new orbitals / OWTTE; σ : overlap of orbitals between nuclei / end-on overlap; π : overlap above and below line joining nuclei / sideways overlap; Award [1] if candidate counts bonds (8 σ, 1 π), or describes all three types of bonds (i.e. C—H is σ, C—C is σ, C=C is σ and π). single bonds longer than double; double bonds stronger than single; 3 C of CH3 is sp ; 2 other two C are sp ; 6 Accept suitable diagrams. 1 [7] 51 (i) 32. Award [1] for each correct Lewis structure. PCl 3 Cl P Cl Cl PCl 5 Cl Cl Cl P Cl Cl POCl 3 O Cl P Cl Cl 3 Accept use of dots or crosses to represent electron pairs. Subtract [1] if non-bonding pair on P in PCl3 is missing. Subtract [1] if non-bonding pair(s) on Cl or O are missing. (ii) PCl3 PCl5 POCl3 trigonal pyramid; trigonal bipyramid; tetrahedral; Accept answers in range 90° and 120°; Accept answers in range 100° to 108°; 100° to 112°; Allow ECF if based on legitimate chemical structure. 6 (iii) PCl3 polar, polarities do not cancel / OWTTE; PCl5 non-polar, polarities cancel / OWTTE; POCl3 polar, polarities do not cancel / OWTTE; 3 Award [2] for three polarities correct, [1] for two polarities correct, and [1] for correct reason(s). Accept argument based on dipole moments. [12] 33. (i) OF2 3 sp ; V-shaped / bent / angular; 2 bonding + 2 non-bonding (electron pairs); (ii) H2CO 2 sp ; trigonal planar; 2 areas of electron density / negative charge centres; (iii) C2 H 2 sp; linear; 2 areas of electron density / negative charge centres; Accept suitable diagrams for shapes. Allow [2] for ECF if correct explanation given for incorrect formula, e.g. C2H4. 3 3 3 [9] 52 34. (i) “head on” overlap of (2) orbitals; along axial symmetry / along a line drawn through the 2 nuclei / OWTTE; Accept suitable diagram for 2nd mark. (ii) parallel p orbitals overlap sideways on; above and below the line drawn through the 2 nuclei / OWTTE; Accept suitable diagram for 2nd mark. (iii) (iv) 1 σ and 1 π / σ and π; 1 σ and 2 π / σ and π; 2 2 1 1 [6] 53 IB2 Revision Topic 5 −1 1. The average bond enthalpy for the C–H bond is 412 kJ mol . Which process has an enthalpy change closest to this value? A. B. C. D. CH4(g) → C(s) + 2H2(g) CH4(g) → C(g) + 2H2(g) CH4(g) → C(s) + 4H(g) CH4(g) → CH3(g) + H(g) −1 2. 3. The mass m (in g) of a substance of specific heat capacity c (in J g What is the heat change in J? A. mct B. mc(t + 273) C. mct 1000 D. mc (t + 273) 1000 Which statements are correct for an endothermic reaction? I. II. III. A. B. C. D. 4. The system absorbs heat. The enthalpy change is positive. The bond enthalpy total for the reactants is greater than for the products. I and II only I and III only II and III only I, II and III Separate solutions of HCl(aq) and H2SO4(aq) of the same concentration and same volume were completely neutralized by NaOH(aq). X kJ and Y kJ of heat were evolved respectively. Which statement is correct? A. B. C. D. 5. −1 K ) increases by t °C . X=Y Y = 2X X = 2Y Y = 3X For which of the following is the sign of the enthalpy change different from the other three? A. CaCO3(s) → CaO(s)+ CO2(g) B. C. D. Na(g) → Na (g) + e CO2(s) → CO2(g) 2Cl(g) → Cl2(g) + − 54 6. Consider the following equations. Mg(s) + H2(g) + 1 2 1 2 ο O2(g) → MgO(s) ∆H = −602 kJ ο O2(g) → H2O(g) ∆H = −242 kJ What is the ∆H° value (in kJ) for the following reaction? MgO(s) + H2(g) → Mg(s) + H2O(g) A. B. C. D. 7. −844 −360 +360 +844 Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a catalyst? I Enthalpy II III A. B. C. D. 8. I only III only I and II only II and III only Using the equations below Cu(s) + 1 2 2Cu(s) + ο O2(g) → CuO(s) ∆H = −156 kJ 1 2 ο O2(g) → Cu2O(s) ∆H = −170 kJ ο what is the value of ∆H (in kJ) for the following reaction? 2CuO(s) → Cu2O(s) + A. B. C. D. 9. 1 2 O2(g) 142 15 –15 –142 When the solids Ba(OH)2 and NH4SCN are mixed, a solution is produced and the temperature drops. Ba(OH)2(s) + 2NH4SCN(s) → Ba(SCN)2(aq) + 2NH (g) + 2H2O(l) Which statement about the energetics of this reaction is correct? A. B. C. D. The reaction is endothermic and ∆H is negative. The reaction is endothermic and ∆H is positive. The reaction is exothermic and ∆H is negative. The reaction is exothermic and ∆H is positive. 55 10. Which type of reaction is referred to in the definition of standard enthalpy change of formation? A. B. C. D. 11. the formation of a compound from its elements the formation of a crystal from its ions the formation of a molecule from its atoms the formation of a compound from other compounds Some chlorine gas is placed in a flask of fixed volume at room temperature. Which change will cause a decrease in entropy? A. B. C. D. adding a small amount of hydrogen adding a small amount of chlorine cooling the flask exposing the flask to sunlight ο 12. ο For a certain reaction at 298 K the values of both ∆H and ∆S are negative. Which statement ο about the sign of ∆G for this reaction must be correct? A. B. C. D. It is negative at all temperatures. It is positive at all temperatures. It is negative at high temperatures and positive at low temperatures. It cannot be determined without knowing the temperature. ο 13. Which reaction has a positive entropy change, ∆S ? A. H2O(g) → H2O(l) B. 2SO2(g) + O2(g) → 2SO3(g) C. CaCO3(s) → CaO(s)+ CO2(g) D. N2(g) + 3H2(g) → 2NH3(g) 14. Which reaction has the most negative ∆H value? ο + − A. LiF(s) → Li (g) + F (g) B. Li (g) + F (g) → LiF(s) C. NaCl(s) → Na (g) + Cl (g) D. Na (g) + Cl (g) → NaCl(s) + – + + ο 15. − − ο The ∆H and ∆S values for a certain reaction are both positive. Which statement is correct about the spontaneity of this reaction at different temperatures? A. B. C. D. It will be spontaneous at all temperatures. It will be spontaneous at high temperatures but not at low temperatures. It will be spontaneous at low temperatures but not at high temperatures. It will not be spontaneous at any temperature. 56 16. Which reaction occurs with the largest increase in entropy? A. B. C. D. 17. Pb(NO3)2(s) + 2KI(s) → PbI2(s) + 2KNO3(s) CaCO3(s) → CaO(s) + CO2(g) 3H2(g) + N2(g) → 2NH3(g) H2(g) + I2(g) → 2HI(g) In aqueous solution, potassium hydroxide and hydrochloric acid react as follows. KOH(aq) + HCl(aq)→ KCl(aq)+ H2O(l) The data below is from an experiment to determine the enthalpy change of this reaction. 3 −3 50.0 cm of a 0.500 mol dm 3 solution of KOH was mixed rapidly in a glass beaker with −3 50.0 cm of a 0.500 mol dm solution of HCl. Initial temperature of each solution = 19.6°C Final temperature of the mixture = 23.1°C (a) State, with a reason, whether the reaction is exothermic or endothermic. ..................................................................................................................................... ..................................................................................................................................... (1) (b) Explain why the solutions were mixed rapidly. ..................................................................................................................................... ..................................................................................................................................... (1) −1 (c) Calculate the enthalpy change of this reaction in kJ mol . Assume that the specific heat capacity of the solution is the same as that of water. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) 57 (d) Identify the major source of error in the experimental procedure described above. Explain how it could be minimized. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) −3 (e) The experiment was repeated but with an HCl concentration of 0.510 mol dm instead −3 of 0.500 mol dm . State and explain what the temperature change would be. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 10 marks) 18. (a) Define the term average bond enthalpy, illustrating your answer with an equation for methane, CH4. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) 58 (b) The equation for the reaction between methane and chlorine is CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g) Use the values from Table 10 of the Data Booklet to calculate the enthalpy change for this reaction. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (c) Explain why no reaction takes place between methane and chlorine at room temperature unless the reactants are sparked, exposed to UV light or heated. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (d) Draw an enthalpy level diagram for this reaction. (2) (Total 10 marks) 59 −1 19. The standard enthalpy change for the combustion of phenol, C6H5OH(s), is −3050 kJ mol at 298 K. (a) Write an equation for the complete combustion of phenol. ...................................................................................................................................... ...................................................................................................................................... (1) (b) The standard enthalpy changes of formation of carbon dioxide, CO2(g), and of water, −1 H2O(l), are −394 kJ mol −1 and −286 kJ mol respectively. Calculate the standard enthalpy change of formation of phenol, C6H5OH(s). ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) ο (c) The standard entropy change of formation, ∆S , of phenol, C6H5OH(s) at −1 298 K is −385 J K −1 mol . Calculate the standard free energy change of formation, ο ∆G , of phenol at 298 K. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (3) 60 (d) Determine whether the reaction is spontaneous at 298 K, and give a reason. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (e) Predict the effect, if any, of an increase in temperature on the spontaneity of this reaction. ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... ...................................................................................................................................... (2) (Total 11 marks) 20. The equation for the decomposition of calcium carbonate is given below. CaCO3(s) → CaO(s) + CO2(g) –1 –1 −1 At 500 K, ∆H for this reaction is +177 kJ mol and ∆S is 161 J K mol . ο (a) Explain why ∆H for the reaction above cannot be described as ∆Hf . ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) State the meaning of the term ∆S. ..................................................................................................................................... ..................................................................................................................................... (1) 61 (c) Calculate the value of ∆G at 500 K and determine, giving a reason, whether or not the reaction will be spontaneous. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 6 marks) 21. Define the term standard enthalpy of formation, and write the equation for the standard enthalpy of formation of ethanol. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… (Total 5 marks) 22. Consider the following reaction. N2(g) + 3H2(g) → 2NH3(g) (i) Using the average bond enthalpy values in Table 10 of the Data Booklet, calculate the standard enthalpy change for this reaction. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (4) 62 (ii) The absolute entropy values, S, at 300 K for N2(g), H3(g) and NH3(g) are 193, 131 and −1 192 JK –1 ο ο mol respectively. Calculate ∆S for the reaction and explain the sign of ∆S . …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (3) ο (iii) Calculate ∆G for the reaction at 300 K. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (1) (iv) If the ammonia were produced as a liquid and not as a gas, state and explain the effect ο this would have on the value of ∆H for the reaction. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (2) (Total 10 marks) 63 ο 23. ο ο Explain in terms of ∆G , why a reaction for which both ∆H and ∆S are positive is sometimes spontaneous and sometimes not. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… (Total 4 marks) 24. Consider the following reaction. N2(g) +3H2(g) → 2NH3(g) ο (i) Use values from Table 10 in the Data Booklet to calculate the enthalpy change, ∆H , for this reaction. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (3) −1 (ii) The magnitude of the entropy change, ∆S, at 27 °C for the reaction is 62.7 J K –1 mol . State, with a reason, the sign of ∆S. …………………………………………………………………………………………… ……………………………………………………………………………………… (2) 64 (iii) Calculate ∆G for the reaction at 27 °C and determine whether this reaction is spontaneous at this temperature. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (3) (Total 8 marks) ο 25. ο ο Explain in terms of AG , why a reaction for which both ∆H and ∆S values are positive can sometimes be spontaneous and sometimes not. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… (Total 4 marks) −1 26. The standard enthalpy change of formation of Al2O3(s) is −1669 kJ mol and the standard −1 enthalpy change of formation of Fe2O3(s) is −822 kJ mol . ο (i) Use these values to calculate ∆H for the following reaction. Fe2O3(s) + 2Al(s) → 2Fe(s) + Al2O3(s) State whether the reaction is exothermic or endothermic. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (3) 65 (ii) Draw an enthalpy level diagram to represent this reaction. State the conditions under which standard enthalpy changes are measured. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (2) (iii) Estimate, without doing a calculation, the magnitude of the entropy change for this reaction. Explain your answer. …………………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… ……………………………………………………………………………………… (3) (Total 8 marks) 27. (a) For the process C6H6(l) → C6H6(s) ο ∆H = −9.83 kJ mol −1 ο –1 –1 and ∆S = −35.2J K mol . Calculate the temperature (in °C) at which ∆G =0 for the above process and explain the significance of this temperature. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (Total 3 marks) 66 1. D 2. 3. 4. 5. 6. A A B D C 17. (b) (c) (d) (e) 18. (b) (c) 7. 8. 9. 10. 11. C A B A C 12. 13. 14. 15. 16. D C B B B (a) exothermic because temperature rises / heat is released; to make any heat loss as small as possible / so that all the heat will be given out very quickly; Do not accept “to produce a faster reaction”. heat released = mass × specific heat capacity × temp increase / q = mc∆T = / 100 × 4.18 × 3.5; = 1463 J / 1.463 kJ; (allow 1.47 kJ if specific heat = 4.2) amount of KOH / HCl used = 0.500 × 0.050 = 0.025 mol; –1 ∆H = (1.463 ÷ 0.025) = −58.5 (kJ mol ); (minus sign needed for mark) Use ECF for values of q and amount used. Award [4] for correct final answer. Final answer of 58.5 or +58.5 scores [3]. Accept 2,3 or 4 significant figures. heat loss (to the surroundings); insulate the reaction vessel / use a lid / draw a temperature versus time graph; 3.5°C / temperature change would be the same; amount of base reacted would be the same / excess acid would not react / KOH is the limiting reagent; (a) energy for the conversion of a gaseous molecule into (gaseous) atoms; (ave54rage values) obtained from a number of similar bonds / compounds / OWTTE; CH4(g) → C(g) + 4H(g); State symbols needed. (bond breaking) = 1890 / 654; (bond formation) = 2005 / 769; –1 enthalpy = –115(kJ mol ) 3 Allow ECF from bond breaking and forming. Award [3] for correct final answer. Penalize [1] for correct answer with wrong sign. molecules have insufficient energy to react (at room temperature) / wrong collision geometry / unsuccessful collisions; extra energy needed to overcome the activation energy / Ea for the reaction; 1 1 4 2 2 [10] 3 2 (d) Ea energy reactants products reaction path exothermic shown; activation energy / Ea shown; Allow ECF from (b). 2 [10] 67 (a) 19. (b) (c) C6H5OH + 7O2 → 6CO2 + 3H2O; Ignore state symbols. ο ο ο ∆Hr =Σ∆Hf products Σ∆Hf reactants; ο −3050 = (6( − 394) +3 (−286) – (∆Hf phenol + O)); ο −1 ∆Hf phenol =−172 kJ mol ; Award [3] for correct final answer. Apply –1 (U) if appropriate. ο −1 Award [2 max] for ∆Hf phenol = +172 kJ mol . (e) 3 appropriate conversion of units; ∆G = –172 – 298(– 0.385) –1 −1 = –57.3 kJ mol / –57 300 J mol ; Award [3] for correct final answer. Accept answers in range –57.0 to –57.3 kJ mol Accept 3 s.f. only. Allow ECF from (b). Apply –1 (U) if appropriate. (d) 1 3 −1 . spontaneous; since ∆G is negative; Allow ECF from (c). reaction becomes less spontaneous; ∆G becomes less negative / more positive; Accept a suitable calculation. Allow ECF from (c). 2 2 [11] 20. ο (a) (cannot be as) conditions are not standard / at 500 K / OWTTE; (cannot be f as) not formation from elements / is decomposition / OWTTE; (b) change in entropy / degree of (dis)order (of system); (c) 2 1 ∆G = 17 7000 − (500 ×161) = +96500; reaction is not spontaneous; ∆G is positive; Allow ECF from calculation for last two marks. 3 [6] 21. enthalpy change associated with the formation of one mole of a compound / substance; from its elements; in their standard states / under standard conditions; 2C(s) + 3H2(g) + 1 2 O2(g) →C2H5OH(l); Award [1] for formulas and coefficients, [1] for state symbols. 5 [5] (i) 22. (ii) (iii) ∆H = (sum of energies of bonds broken) – (sum of energies of bonds formed); Can be implied by working. Correct substitution of values and numbers of bonds broken; Correct substitution of values and numbers of bonds made; (∆H = (N≡≡N) + 3(H—H) − 6(N—H) = 944 + 3(436) − 6(388) =) −76 (kJ); 4 Allow ECF. Do not penalize for SF or units. ο ∆S = (sum of entropies of products) – (sum of entropies of reactants); Can be implied by working. −1 –1 (= 2 × 192 – (193 + 3 × 131) =) −202(J K mol ); four molecules make two molecules / fewer molecules of gas; ο ο ο −1 (∆G =∆H – T∆S = −76.0 − 300( 0.202)) = − 15.4 (kJ mol ); 3 1 PAGE \*Arabic 18 (iv) Do not penalize for SF. ο ∆H becomes more negative; heat released when gas → liquid; 2 [10] 23. ο a reaction is spontaneous when ∆G is negative; ο at high T, ∆G is negative; ο ο −T∆S is larger / greater than ∆H ; ο ο ο at low T, ∆G is positive because −T∆S is smaller than ∆H / OWTTE; 4 [4] (i) selection of all the correct bonds or values from Data Booklet; ∆H = (N≡≡N) + 3(H—H) − 6(N—H)/944 + 3(436) − 6(388); = −76 (kJ); 3 Allow ECF for one error (wrong bond energy / wrong coefficient / reverse reaction) but not for two errors (so –611, –857, +76, +1088 all score 2 out of 3). 24. (ii) (iii) negative; decrease in the number of gas molecules / OWTTE; ∆G = ∆H − T∆S ∆G = −76.0 − 300 (−0.0627); Award [1] for 300 K. Award [1] for conversion of units J to kJ or vice versa. Allow ECF from c(i) from ∆H. Allow ECF from c(ii) for sign of ∆S. −1 = −57.2 (kJ mol ) is spontaneous / or non-spontaneous if positive value obtained; [3 max] 2 3 [8] 25. ο ο a reaction is spontaneous when ∆G is negative / non-spontaneous when ∆G is positive; ο at high T, ∆G is negative; ο ο (because) T∆S is greater than ∆H ; ο ο ο at low T, ∆G is positive because T∆S is smaller than ∆H / OWTTE; 4 [4] 26. (i) ∆H = ∆Hf (products) −∆Hf (reactants) /= (−1669) − (–822) = −847 kJ Ignore units; exothermic (ECF from sign of ∆H) ; (ii) 2 3 Reactants enthalpy / energy ignore lines connecting reactants and products Products (iii) [1] for the diagram ECF from sign of ∆H in (i) 298 K / 25°C AND 1 atm / 101(.3) kPa; Both needed for the mark. entropy change will be zero / very small; (structure of / bonding in) reactants and products similar / only solids involved; the disorder / randomness will not change; 3 [8] PAGE \*Arabic 18 27. ο ο ο (∆G = ∆H − ∆S = 0) ο as T increases, − T∆S becomes larger / more positive; ∆G increases / becomes more positive / less negative; process becomes less spontaneous / reverse reaction favoured; ο ο ο (∆G = ∆H − T∆S = 0) 9830 − mol J–1 H ∆ ∆ S –35.2 JK mol = therefore, T 1–; = 279 K = 6°C; (no SF penalty) ECF (ECF if kJ used above) temperature at which solid and liquid are in equilibrium with each other / melting point / freezing point / T at which it changes from spontaneous to non-spontaneous or vice-versa / T at which no (useful) work is done; 3 [3] PAGE \*Arabic 18 IB2 Revision 1. Which statement is correct about the behaviour of a catalyst in a reversible reaction? A. B. C. D. 2. It decreases the enthalpy change of the forward reaction. It increases the enthalpy change of the reverse reaction. It decreases the activation energy of the forward reaction. It increases the activation energy of the reverse reaction. In the Haber process for the synthesis of ammonia, what effects does the catalyst have? A. B. C. D. 3. Topic 6 Rate of formation of NH3(g) Increases Increases Increases No change Amount of formed NH3(g) Increases Decreases No change Increases Which statement is correct for the reaction below? 4P + Q → 2R + 2S A. B. C. D. 4. For a given reaction, why does the rate of reaction increase when the concentrations of the reactants are increased? A. B. C. D. 5. The rate of formation of R is one half the rate of the disappearance of Q. The rate of disappearance of Q is one quarter of the rate of disappearance of P. The rates of formation of R and S are not equal. The rate of formation of S is double the rate of disappearance of P. The frequency of the molecular collisions increases. The activation energy increases. The average kinetic energy of the molecules increases. The rate constant increases. Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a catalyst? Enthalpy I II III A. B. C. D. I only III only I and II only II and III only PAGE \*Arabic 18 6. Based on the definition for rate of reaction, which units are used for a rate? −3 A. mol dm −1 B. mol time −1 C. dm time –3 –1 D. mol dm time 7. The rate expression for a particular reaction is Rate = k[P][Q] Which of the units below is a possible unit for k? A. B. C. D. 8. –2 6 –1 mol dm min –1 3 –1 mol dm min 3 –1 mol dm min –2 –6 –1 mol dm min Which step is included in the definition of the term rate determining step? A. the step with the slowest moving particles B. the step with the fewest reactant particles C. the slowest step in a reaction (iii) the last step in a reaction (iv) 9. For the chemical reaction 2NO(g) + O2(g) → 2NO2(g) the following reaction mechanism has been proposed. NO (g) + NO(g) N2O2 (g) N2O2 (g) + O2 (g) → 2NO2 (g) fast slow What could be the rate expression for this reaction? A. B. C. D. rate = k[NO][O2] 2 rate = k[NO] rate = k[N2O2][O2] 2 rate = k[NO] [O2] PAGE \*Arabic 18 10. Consider the following statements. I. The rate constant of a reaction increases with increase in temperature. II. Increase in temperature decreases the activation energy of the reaction. III. The term A in the Arrhenius equation ( k = Ae requirements of the collisions. − Ea RT ) relates to the energy Which statement(s) is/are correct? A. B. C. D. 11. For a given reaction, why does the rate of reaction increase when the concentrations of the reactants are increased? A. B. C. D. 12. The frequency of the molecular collisions increases. The activation energy increases. The average kinetic energy of the molecules increases. The rate constant increases. Values of a rate constant, k, and absolute temperature, T, can be used to determine the activation energy of a reaction by a graphical method. Which graph produces a straight line? A. B. C. D. 13. I only II only I and III only II and III only k versus T 1 k versus T ln k versus T 1 ln k versus T What is the definition of half-life for a first order reaction? A. B. C. D. The time required for the quantity of a reactant to decrease by half. Half the time required for a reactant to be completely used up. Half the time required for a reaction to reach its maximum rate. The time required for a reaction to reach half of its maximum rate. PAGE \*Arabic 18 (a) 14. Identify two features of colliding molecules that react together in the gas phase. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (b) For many reactions, the rate approximately doubles for a 10°C rise in temperature. State two reasons for this increase and identify which of the two is the more important. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (3) (Total 5 marks) 15. When excess lumps of magnesium carbonate are added to dilute hydrochloric acid the following reaction takes place. MgCO3(s) + 2HCl(aq) → MgCl2(aq) + CO2(g) + H2O(l) (a) Outline two ways in which the rate of this reaction could be studied. In each case sketch a graph to show how the value of the chosen variable would change with time. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) PAGE \*Arabic 18 (b) State and explain three ways in which the rate of this reaction could be increased. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (6) (c) State and explain whether the total volume of carbon dioxide gas produced would increase, decrease or stay the same if (i) more lumps of magnesium carbonate were used. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (2) (ii) the experiments were carried out at a higher temperature. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (2) (Total 14 marks) PAGE \*Arabic 18 16. The reaction between ammonium chloride and sodium nitrite in aqueous solution can be represented by the following equation. NH4Cl(aq) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq) The graph below shows the volume of nitrogen gas produced at 30 second intervals from a mixture of ammonium chloride and sodium nitrite in aqueous solution at 20°C. 140 120 100 Volume of N 2 / cm 3 80 60 40 20 0 0 20 40 60 80 100 120 140 160 180 Time / s (a) (i) State how the rate of formation of nitrogen changes with time. Explain your answer in terms of collision theory. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (2) (ii) Explain why the volume eventually remains constant. ............................................................................................................................ ............................................................................................................................ (1) PAGE \*Arabic 18 (b) (i) State how the rate of formation of nitrogen would change if the temperature were increased from 20°C to 40°C. ............................................................................................................................ ............................................................................................................................ (1) (ii) State two reasons for the change described in (b)(i) and explain which of the two is more important in causing the change. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (3) (iii) The reaction between solid ammonium chloride and aqueous sodium nitrite can be represented by the following equation. NH4Cl(s) + NaNO2(aq) → N2(g) + 2H2O(l) + NaCl(aq) State and explain how the rate of formation of nitrogen would change if the same amount of ammonium chloride were used as large lumps instead of as a fine powder. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (2) (Total 9 marks) PAGE \*Arabic 18 17. The following reaction 2N2O5(g) → 4NO2(g) + O2 (g) is described as first order with respect to N2O5. (a) Write the rate expression for the reaction. ...................................................................................................................................... (1) (b) One possible mechanism for this reaction is given below. N2O5(g) → NO(g) + NO3(g) Step 1 N2O5(g) + NO3(g) → 2NO2(g) + O2(g) Step 2 Describe the rate expression that would result if the rate determining step in the mechanism is (i) Step 1. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (1) (ii) Step 2. ............................................................................................................................ ............................................................................................................................ ............................................................................................................................ (2) Outline your reasoning. (c) Explain what is meant by the term half-life for this reaction. ...................................................................................................................................... ...................................................................................................................................... (1) PAGE \*Arabic 18 (d) State what is characteristic about the half-life of a first order reaction. ...................................................................................................................................... ...................................................................................................................................... (1) (Total 6 marks) 18. (a) Nitrogen monoxide may also be converted into nitrogen dioxide at high temperature according to the equation below. NO(g) + CO(g) + O2(g) → NO2(g) + CO2(g) (i) Sketch a graph of concentration of NO2(g) produced against time for this reaction and annotate the graph to show how the initial rate of reaction could be deduced. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (3) (ii) The results from a series of experiments for this reaction are shown below. Deduce, giving a reason, the order of reaction with respect to each of the reactants. Experiment [NO(g)] / [CO(g)] / [O2(g)] / −3 mol dm −3 mol dm −3 mol dm 1 1.00 × 10 2 2.00 × 10 3 2.00 × 10 4 4.00 × 10 −3 −3 −3 −3 1.00 × 10 1.00 × 10 2.00 × 10 1.00 × 10 −3 −3 −3 −3 1.00 × 10 1.00 × 10 1.00 × 10 2.00 × 10 −1 −1 −1 −1 Initial rate / mol dm −3 −1 s 4.40 × 10 1.76 × 10 1.76 × 10 7.04 × 10 −4 −3 −3 −3 PAGE \*Arabic 18 …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (6) (b) Explain why the order of a reaction cannot be obtained directly from the stoichiometric equation. …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (c) (i) First order reactions have a constant half-life. Define the term half- life and explain why it is constant for first order reactions. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (2) (ii) The value of k for a first order reaction is 440 s −1 . Calculate the half-life for this reaction. …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (1) (Total 13 marks) PAGE \*Arabic 18 19. Oxygen and nitrogen monoxide react together to form nitrogen dioxide. O2(g) + 2NO(g) → 2NO2(g) The graph below shows how the initial rate of reaction changed during an experiment in which the initial [NO(g)] was kept constant whilst the initial [O2(g)] was varied. Rate [O 2 (g)] (a) Deduce, giving a reason, the order of reaction with respect to O2 …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) (b) In a series of experiments, the initial [O2(g)] was kept constant while the initial [NO(g)] was varied. The results showed that the reaction was second order with respect to NO. Sketch a graph to show how the rate of reaction would change if the initial [NO(g)] was increased. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (2) PAGE \*Arabic 18 (c) Deduce the overall order of this reaction. …………………………………………………………………………………………… …………………………………………………………………………………………… (1) (d) State and explain what would happen to the initial rate of reaction if the initial concentration of NO was doubled and that of O2 was halved. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (3) (e) When the initial values are [O2(g)] = 1.0 × 10 mol dm –3 −2 , the initial rate of reaction is 6.3 × 10 mol dm −4 –3 mol dm and [NO(g)] = 3.0 × 10 −2 –3 –1 s . Write the rate expression for this reaction and calculate the rate constant, stating its units. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… (4) (Total 12 marks) PAGE \*Arabic 18 20. Gaseous hydrogen iodide, HI, decomposes into its elements when heated. The decomposition was investigated in a series of experiments carried out at the same temperature. The following data was obtained. Experiment number 1 2 3 4 (a) −3 Initial (HI) / mol dm −3 2.2 × 10 −3 6.6 × 10 −2 2.2 × 10 −3 4.4 × 10 −3 −1 Initial rate of reaction / mol dm s −6 1.1 × 10 −6 9.9 × 10 −4 1.1 × 10 to be determined Write the equation for the decomposition of hydrogen iodide. ..................................................................................................................................... (1) (b) Deduce the order of the reaction and explain your answer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (c) State the rate expression for the reaction. ..................................................................................................................................... (1) (d) Determine the initial rate of reaction in experiment 4. ..................................................................................................................................... ..................................................................................................................................... (1) (e) Define the term molecularity and deduce its value in this reaction. ..................................................................................................................................... ..................................................................................................................................... (2) (Total 7 marks) PAGE \*Arabic 18 21. Nitrogen(II) oxide reacts with hydrogen as shown by the following equation. 2NO(g) + 2H2(g) → N2(g) + 2H2O(g) The table below shows how the rate of reaction varies as the reactant concentrations vary. Initial [NO] / Experiment (a) mol dm Initial /[H2]mol –3 dm –3 Initial rate / –3 –1 mol N2 dm s –6 1 0.100 0.100 2.53 × 10 2 0.100 0.200 5.05 × 10 3 0.200 0.100 –6 10.10 × 10 4 0.300 0.100 –6 22.80 × 10 –6 Determine the order of reaction with respect to NO and with respect to H2. Explain how you determined the order for NO. NO .............................................................................................................................. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... H2 ................................................................................................................................ ..................................................................................................................................... (3) (b) Write the rate expression for the reaction. ..................................................................................................................................... (1) (c) Calculate the value for the rate constant, including its units. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) PAGE \*Arabic 18 (d) A suggested mechanism for this reaction is as follows. H2 + NO X fast step X + NO → Y + H2O slow step Y + H2 → N2 + H2O fast step State and explain whether this mechanism agrees with the experimental rate expression in (b). ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (4) (e) Explain why a single step mechanism is unlikely for a reaction of this kind. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (f) Deduce how the initial rate of formation of H2O(g) compares with that of N2(g) in experiment 1. Explain your answer. ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... ..................................................................................................................................... (2) (Total 14 marks) PAGE \*Arabic 18 22. (a) The following data were obtained for the reaction of nitrogen monoxide gas, NO(g), with oxygen gas to form nitrogen dioxide gas, NO2(g), at 25 C. [NO]/ [O2]/ Experiment −3 mol dm −3 mol dm 1 0.50 0.20 3.0 × 10 2 0.50 0.40 6.0 × 10 3 1.00 0.80 4.8 × 10 (i) −3 −1 Initial rate /mol dm s −3 −3 −2 Calculate the order with respect to the two reactants and write the rate expression for the reaction. Show your reasoning. ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (5) (ii) Explain why the following mechanism is not consistent with the rate expression. NO (g) + O2 (g) → NO2(g) + O (g); slow step NO (g) + O (g) → NO2 (g); fast step ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) PAGE \*Arabic 18 (iii) Explain why the following mechanism is consistent with the rate expression, but is unlikely. 2NO(g) +O2 (g) → 2NO2 (g) ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (2) (iv) Explain why the following mechanism is consistent with the rate expression. NO (g) + O2(g) → NO3 (g); fast NO3 (g) + NO (g) → 2NO2 (g); slow ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (3) (Total 12 marks) PAGE \*Arabic 18 1. 2. 3. 4. 5. C C B A C 14. (b) 6. 7. 8. 9. 10. 11. 12. 13. A D A (a) molecules must have sufficient/minimum energy / energy ≥ activation energy; appropriate collision geometry / correct orientation; increased frequency of collisions / collisions more likely; Not just “more collisions”, there must be a reference to time. increased proportion of molecules with sufficient energy to react / E ≥ Ea; Not “activation energy is reduced”. Proportion of molecules with E ≥ Ea is more important; (dependent on correct second marking a point); (a) 15. D B C D A measure volume of carbon dioxide / CO2 / gas produced / measure pH; 2 3 [5] 4 starts at origin and levels off measure mass of chemicals / apparatus; starts high and decreases Graph should show increase as reaction progresses (as HCl is consumed). (b) Method 1 use powdered MgCO3 / OWTTE; particles collide more frequently / increased surface area / OWTTE; Method 2 increase (reaction) temperature / heat / warm; more of the collisions are successful / more particles with E > Ea / OWTTE; Method 3 increase acid concentration; more frequent (reactant) collisions; Method 4 add catalyst; lowers activation energy/ Ea / OWTTE; Award [2] each for any three methods (c) (ii) 6 max (i) stays the same; MgCO3 was already in excess; stays the same; same quantities of reactants used; 2 2 [14] PAGE \*Arabic 18 16. (ii) (b) (ii) (iii) (a) (i) it is decreasing; less frequent collisions / fewer collisions per second or (unit) time; reactant(s) used up / reaction is complete; Do not accept reaction reaches equilibrium. (i) it would increase; Accept a quantitative answer such as “doubles”. more frequent collisions; collisions or molecules have more energy (OWTTE); more molecules with energy ≥ Ea; rate would be lower; smaller surface area; 2 1 1 3 2 [9] (a) 17. (b) (ii) (c) (d) 1 rate = k [N2O5]/ k [N2O5] ; (i) Rate ×[N2O5] One molecule of [N2O5]; Rate ×[N2O5] [NO3] But NO3 comes from N2O5 in first step 2 So:Rate ×[N2O5] 2 the time taken for the concentration/amount (of N2O5) to decrease to half its original value / OWTTE; it is constant / does not depend on concentration (of reactant); (a) 18. 1 1 1 1 [6] (i) [NO 2 (g)] time (ii) (b) (c) correct axes; curve starts at origin and levels off; tangent to curve at origin; second order with respect to NO; (Expt 1+2) double [NO(g)] only and rate quadruples; zero order with respect to CO; (Expt 2+3) double [CO(g)] only and rate is unchanged; zero order with respect to O2; (Expt 2+4) double both [NO(g)] and [O2(g)] and rate quadruples; 3 6 stoichiometric equation gives no indication of the reaction mechanism / OWTTE; 1 (i) time taken for the concentration of a reactant to fall to half of its initial value; half-life of a first order reaction is independent of the original concentration; (ii) .6 0693 93 −3 t= = 1.58 ×10 (s); k440 1 2 2 1 [13] (a) 1 / first order; rate is (directly) proportional to concentration of oxygen / OWTTE; 19. 2 (b) rate [NO(g)] correct axes; correct shape curve; 2 (c) 3 / third order; Allow ECF from (a) and (b). (d) overall effect on rate = 4 × 2 / doubled / × 2; [NO(g)]doubled, rate = × 4 / quadrupled; [O2(g)] halved, rate = × 1 / halved; Allow ECF from (a) and (b). 2 rate = k[NO(g)] [O2(g)]; (e) 1 1 k= 3 rate 6.3 × 10−4 = ; 2 [ NO ( g )] [O2 ( g )] (3.0 × 10 − 2 ) 2 (1.0 × 10 − 2 ) = 70; –2 6 –1 mol dm s ; Allow ECF. State symbols not needed. 4 [12] (a) 20. (b) (c) (d) (e) 2HI → H2 + I2; Ignore state symbols. 2; when [HI] is trebled, rate increases ×9/ OWTTE; Accept equivalent argument based on experiments 1 and 3. 2 rate = k[HI] ; 1 ECF from (b) −6 4.4 ×10 ; (ignore units) ECF from (b) 1 2 1 the number of molecules taking part in the slowest or rate-determining step of a reaction / OWTTE; 2; 2 [7] 21. (b) (c) (a) (order with respect to) NO = 2; (order with respect to) H2 = 1; rate increases ×4 when [NO] doubles / OWTTE; 2 rate = k[NO] [H2]; ECF from (a). –3 –1 –3 2 −3 mol dm s = k (0.100 mol dm ) (0.100 mol dm )) –3 k = 2.53 × 10 ; −2 6 –1 mol dm s ; ECF from (b). (2.53 × 10 3 1 −6 1 1 (d) Or agrees / yes; slow step depends on X and NO; X depends on H2 and NO; (so) NO is involved twice and H2 once; Overall equation matches the stoichiometric equation; Award [1] each for any three of the four above. OWTTE ECF for “no”, depending on answer for (b). 4 max agrees / yes; [X] and [H ][NO] = constant; 2 rate of slow step = k [X][NO] 2 = k [H2][NO] ; ECF for “no”, depending on answer for (b). (e) (f) reaction involves four molecules; statistically / geometrically unlikely; the rate of formation of H2O(g) = 2 × rate for N2(g); because 2 moles H2O formed with 1 mole N2 / OWTTE; 4 2 2 [14] 22. (ii) (iii) (iv) (i) [NO] constant, [O2] doubles, rate doubles; rate ∝ [O2]/ first order; [NO] doubles, [O2] doubles, rate increases 8 times; 2 rate ∝ [NO] / second order; 2 2 rate = k [NO] [O2] / rate ∝ [NO2] [O2]; slow step / rate determining step involves only one NO and one O2; not two NO and one O2 (as required by rate-expression); 2 since two NO and one O2 involved in the (one step) mechanism, correct O2 rate expression possible; but unlikely that three particles will collide at the same time; 2 from fast step depends on [NO3] depends on [NO] and [O2]; rate depends on [NO3] and [NO]; 2 thus rate must depend on [NO] [NO2] (consistent with rate expression); 3 5 [12]
