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Kinetics Workbook for Chemistry 12 Period 1 2 3 4 5 6 7 8 9. Monitoring Reaction Rates Factors that Change the Rate Collision Theory PE Diagrams Mechanisms Lab: The Iodine Clock Reaction Review Review Test Worksheets Quiz WS 1 WS 2 WS 3 WS 4 WS 5 Internet Review Practice Test 1 Practice Test 2 Q1 Q2 Q3 Q4 Q5 This workbook will allow you to demonstrate your understanding of all aspects of the kinetics unit. The minimum expectation is that you do all of these questions by the due dates given by your teacher. Do the questions. Use your notes from class to assist you. Then after you have finished go to the web site to evaluate your work. Make a list of those things that you do not quite understand and bring them to class. Your instructor will review them. There are other things that you should do to prepare for the test at the end of the unit. Remember, what you put into this course is what you will get out. There is no substitute for consistent effort and hard work. If you cannot do a question, get some help before the end of the unit, you need to know, understand, and remember everything. Good luck! I know you can do well in this unit. 1 WS #1 1. 2. 2. 3. i) Monitoring and Calculating Reaction Rates Read the chapter from your textbook on Kinetics over the next week. “A” students should read it twice. a) When measuring a property associated with a reactant in a reaction, does it increase or decrease? b) When measuring a property associated with a product in a reaction, does it increase or decrease? Give three ways to measure the rate of the following reaction. State the specific properties that you would monitor and include units (amount is not a specific property). State if each property would increase or decrease. Describe in each case how you would calculate the reaction rate. 2HNO3(aq) + Cu(s) → NO2(g) The first one is done for you. + H2O(l) + CuNO3(aq) Mass of Cu Decrease Grams Rate = mass/time ii) iii) 4. Calculate the rate in units of (g Cu/min). Mass of copper (g) 3.26 Time (min) 5.0 2.93 7.0 2.61 9.0 5. Calculate the rate in units of (mole Cu/min). 6. Calculate the rate in moles HNO3 consumed per second (remember that 2 moles are consumed per 1 mole of Cu). 7. Calculate the rate in units of (g/sec) for HNO3. 8. Calculate the rate in units of (mL NO2/sec). 2HNO3(aq) + Cu(s) → NO2(g) + H2O(l) + CuNO3(aq) Volume of NO2 (mL) 10.0 11.5 Time (sec) 0.00 5.00 9. 12.7 10.00 Calculate the rate in units of (L NO2/min). 2 10. Calculate the rate in units of (moles NO2/min) at STP. 11. Calculate the rate in units of (moles HNO3/min) at STP (remember that 2 moles are consumed per 1 mole of NO2) 12. Calculate the rate of the following reaction: 2NO (g) + 2H2 (g) → N2 (g) + 2H2O (g) mole NO Time(s) 0.080 0.060 0.040 0.020 0.00 2.0 4.0 6.0 8.0 10.0 12.0 a) What is the rate in moles NO per second? b) What is the rate in moles N2 per second? 3 c) What is the rate in grams NO per min? d) What is the rate in grams N2 per hour? 13. Choose three properties that you could measure in order to monitor the rate of the following reaction. Cu (s) + 2AgNO3 (aq) → 2 Ag (s) + Cu(NO3)2 (aq) Property Unit of Measurement Change i. ii. iii. 14. Calculate the rate of the following reaction in units of M/s: Zn(s) + 2HCl(aq) → ZnCl2(aq) + Molarity of HCL (M) time (seconds) 15. 0.612 21.0 0.813 25.0 1.05 29.0 Calculate the rate of the following reaction in L/min: Zn(s) + 2HCl(aq) 16. H2(g) → ZnCl2(aq) + H2(g) Volume of H2 (L) 0.255 0.550 0.790 Time (min) 1.0 2.0 3.0 If 0.369 g of HCl is neutralized with 0.250 M NaOH in 25.0 seconds, what is the reaction rate in moles HCl /min. 4 WS # 2 Factors That Change The Reaction Rate Homogeneous reactions Reactants are in the same phase (aq), (g) , or (l) and are thoroughly mixed. Heterogeneous reactions Reactants are in the two or more phases and are not thoroughly mixed (two solids do not mix). Classify as Homogeneous or Heterogeneous: 1. Zn(s) + 2 HCl(aq) → H2 (g) + ZnCl2 (aq) 2. Ag+(aq) + Cl-(aq) → AgCl (s) 3. H2(g) + F2(g) → 2HF(g) 4. 2Al(s) + 3I2(s) → 2AlI3(s) The following four factors will increase the rate of a chemical reaction that is homogeneous: 1. 2. 3. 4. The above four factors as well as the two below will increase the rate of a heterogeneous reaction: 5. 6. For each reaction specifically describe all of the ways to increase the reaction rate (i.e.. increase [H2]). 1. H2 (g) + F2 (g) → 2 HF (g) 2. 3. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O (l) Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq) 5 4. State three examples of chemical reactions that are desired to be slow. 5. Give three examples of chemical reactions that are desired to be fast. 6. List all of the ways to increase the rate of the following reaction: 2H2O2(aq) → 2H2O(l) + O2(g) I. Homogeneous reactions are generally faster than heterogeneous- the reactants are mixed better and therefore there are more collisions between reactant particles. HCl(aq) + NaOH(aq) → is Zn(s) + 2HCl(aq) II. NaCl(aq) + H2O(l) faster than → H2(g) + ZnCl2(aq) Simple ionic reactions (where there are no bonds to break) are generally faster than more complex ionic reactions (where there are bonds to break). Pb+2(aq) + 2Cl-(aq) → PbCl2(l) is faster than 2Na+(aq) + 2ClO-(aq) → 2Na+(aq) + 2Cl-(aq) + O2(g) Solid reactants are slower than gases, which are slower than aqueous. 1. Indicate the faster and slower reaction and explain why. a) 2Al(s) + 3I2(s) → 2AlI3(s) b) Ag+(aq) + Cl-(aq) → AgCl(s) 6 2. Indicate the faster and slower reaction and explain why. a) 2Al(s) + 3I2(s) b) 2Na+(aq) + 2ClO-(aq) → 3. Indicate the faster and slower reaction and explain why. a) 3Ba+2(aq) + 2PO4-3(aq) b) Cu(s) + 2Ag+(aq) WS # 3 1. → 2AlI3 (s) 2Na+(aq) + 2Cl-(aq) → → + O2(g) Ba3(PO4)2(aq) Cu+2 (aq) + 2Ag(s) Collision Theory 2. Chemical reactions are the result of _________________ between reactant particles, where _________________ are broken and new ones form. A successful collision requires _____________________ and __________________ . 3. Describe as fast, medium or slow. Explain! i) 2 H2 (g) + O2 (g) _______ _______ 4. 2 H20 (l) (room temperature) _______________________________________________________ 2 Ag+ (aq) + CO32- (aq) ii) iii) → → Ag2CO3 (s) _______________________________________________________ 2 HCl (aq) + Na2CO3 (aq) → CO2 (g) + 2 NaCl (aq) + H20 (l) _______ _______________________________________________________ i) Describe how you would measure the rate of the reaction : Zn(s) + 2 HCl(aq) ii) → ZnCl2(aq) + H2(g) ________________________________________________________________ List four ways to increase the rate. ________________________________________________________________ ________________________________________________________________ 7 5. A 10 °C temperature increase frequently doubles the rate of a slow reaction because: a) The temperature has doubled. b) The PE of the colliding particle has doubled. c) The KE of the colliding particle has doubled. d) The fraction of particles with sufficient KE to react has doubled. 6. Both collisions A and B have the same KE. Which collision is successful and explain why. Before Collision After Collision A) B) ________________________________________________________________ ________________________________________________________________ 7. Use the collision theory to explain how each factor increases the reaction rate. i) Increasing temperature ii) iii) iv) v) Increasing [reactants] Increasing surface area (solid) Agitation of a heterogeneous reaction Adding a catalyst i) _________________ _________________ ii) _________________ iii) _________________ iv) _________________ v) _________________ _________________ 8 8. Explain why collision A was successful while collision B was unsuccessful. Before Collision After Collision A) B) ________________________________________________________________ ________________________________________________________________ Explain each of the following using the collision theory. You need to explain each statement. 9. A candle is not burning at room temperature A match lights the candle The candle continues to burn 10. H2O2 decomposes slowly at 20o C KI is added and rapid decomposition begins The temperature increases 11. H2 and O2 in a balloon do not react A spark ignites the balloon 9 An explosion results 12. CH4 and O2 in a balloon do not react A platinum gauze ignites the balloon An explosion results 13. N2(g) + O2(g) → 2NO(g) Even though there are more than four billion collisions per second between N and O the amount of product after a year is too small to detect. Using the collision theory, give two reasons why this reaction might be slow. i) ii) 14. Give two reasons why some collisions will not result in a chemical reaction. i) ii) 15. Give five reasons that might account for the following reaction having a high rate. Ca (s) + 2HCl (aq) → CaCl2 (aq) + H2 (g) i) ii) iii) iv) v) 16. C(s) + O2(g) → CO2(g) List four ways the rate of the reaction could be increased. i) ii) iii) iv) 10 17. State the relationship between Activation energy and the rate of a reaction. Graph the relationship. Rate Activation Energy 18. State the relationship between Temperature and the rate of a reaction. Graph the relationship. Rate Temperature 19. State the relationship between Concentration and the rate of a reaction. Graph the relationship. Rate Molarity 11 20. Give three examples of reactions that are desired to be slow. a) b) c) 21. Give three examples of reactions that are desired to be fast. a) b) c) 22. List all of the ways to increase the rate of the reaction: 2 H2O2(aq) → 2 H2O(l) + O2(g) 23. Describe how you could measure the rate of the reaction above. State the property you would measure and describe how it changes. Draw a diagram to illustrate your answer. 24. Pick the fastest and the slowest reaction at 20 °C. a) H2(g) + I2(g) → 2 HI(g) b) 2 HCl(aq) + Na2CO3(aq) 2+ c) Hg (aq) + 2 I -(aq) → → CO2(g) + 2 NaCl(aq) + H2O(l) HgI2(s) 25. H2 and O2 can exist at 20 °C for years without reacting. But when a small spark ignites the mixture it reacts explosively. Explain using the Collision Theory. 26. Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and the x-axis is collision energy. Draw the Ea line showing about 10% of the collisions 12 having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy. Faction of collisions Collision Energy 27. Shade in the area of the collision energy distribution diagram showing those collisions that do not have the required energy to be successful at the temperature below. Faction of collisions Collision Energy Ea 26. Shade in the area of the collision energy distribution diagram showing those collisions that do have the required energy to be successful at the temperature below. Redraw the curve at a higher temperature. 13 Faction of collisions Collision Energy Ea Kinetics - Descriptions Use the collision theory to explain the following. Each sentence must be explained with a statement from the collision theory. 1. A unlit candle does not burn. It burns after being lit with a match. It continues to burn. 2. A solution is reacting very slowly to produce bubbles. KI is added and although it is not consumed in the reaction, it speeds up the reaction rate. The temperature increases. The rate increases even more. 14 3. Iron reacts slowly with HCl. Iron is replaced with Zn and a much more vigorous reaction rate occurs. 4. H2 and O2 can exist together for years at room temperature without reacting. A spark begins the reaction. An explosion results. 5. Dilute nitric acid shows little reaction with copper. Concentrated nitric acid vigorously reacts. 6. Water puts out a fire. 7. Paint prevents rusting. 8. A preservative in food slows rotting. 15 WS # 4 1. Potential Energy Diagrams Worksheet Draw the PE diagram showing the PE changes that occur during a successful collision of the exothermic reaction: H2 + I2 → 2 HI + 250 kJ The PE of the reactants = 400 kJ Ea = 200 kJ PE Reaction Path 2. Draw the PE diagram showing the PE changes that occur during a successful collision of the endothermic reaction: A + B + 200 kJ → C The PE of the reactants = 200 kJ The Activation Energy in the forward direction = 250 kJ PE Reaction Path 16 3. Write the following reaction in ΔH notation. A + B + 200 kJ → 4. Write the following reaction in Standard Notation. H2 5. + I2 → 2 HI ΔH = -250 kJ Write in Standard Notation. 2NI3 + 3BaCl2 → 6. C 2NCl3 + 3BaI2 ΔH = 175 kJ Write in ΔH notation. 2AlBr3 + 3BaF2 → 2AlF3 + 3BaBr2 + 276 kJ Draw the potential energy diagram for the following reactions. 7. Potential energy of reactants = Potential Energy of activated complex = Potential Energy of the products = 250 kJ 350 kJ 300 kJ PE Reaction Path 17 a) b) c) d) e) f) g) h) How does the potential energy change as the reaction proceeds? How does the kinetic energy change as the reaction proceeds? Is the reaction exothermic or endothermic? What is the value of ΔH? If a catalyst was added, what would happen to the potential energies of the: Reactants? Products? Activated Complex? If a catalyst were added what would happen to the rate? Draw the potential energy diagram for the following reactions. 8. Potential energy of reactants = Activation Energy = 350 kJ 100 kJ PE Reaction Path Potential Energy of the products = a) b) c) d) 250 kJ How does the potential energy change as the reaction proceeds? How does the kinetic energy change as the reaction proceeds? Is the reaction exothermic or endothermic? What is the value of ΔH? If the concentration of the reactants was increased, what would happen to the energies of the: e) f) g) h) Reactants? Products? Activated Complex? What would happen to the rate? 18 Draw the potential energy diagram for the following reactions. PE 9. Potential energy of reactants = Potential Energy of activated complex = ΔH = a) b) c) d) How does the potential energy change as the reaction proceeds? How does the kinetic energy change as the reaction proceeds? Is the reaction exothermic or endothermic? What is the value of ΔH? If the temperature was increased, what would happen to the energies of the: Reactants? Products? Activated Complex? What would happen to the rate? e) f) g) h) 200 kJ 400 kJ 150 kJ Reaction Path 19 PE Reaction Path 10. Potential energy of products = Potential Energy of activated complex = ΔH= a) b) c) d) 50 kJ 400 kJ -50 kJ How does the potential energy change as the reaction proceeds? How does the kinetic energy change as the reaction proceeds? Is the reaction exothermic or endothermic? What is the value of ΔH? If the surface area of the reactants was increased, what would happen to the energies of the: e) f) g) h) Reactants? Products? Activated Complex? What would happen to the rate? 11. What is the only thing, other than changing the reaction that will change the potential energy diagram? Describe how it will affect the diagram and the rate. 20 12. Label each interval on the potential energy diagram. a b c d e a) PE b) c) d) Reaction Path e) 13. Label each interval on the potential energy diagram. a b c d e PE Reaction Path a) b) c) d) e) 21 Ws # 5 Mechanisms → → → OCl- + H2O HOCl + IHOI + OH- 1. i) ii) iii) HOCl + OHHOI + ClH2O + OI- The net chemical equation is: The reaction intermediates are: The catalyst is: Br2 → Br + OCl2 Br + Cl 2. 2Br → → BrOCl + BrCl Cl fast slow fast i) ii) iii) iv) The net chemical equation is: The reaction intermediates are: The rate-determining step is If the concentration of Br2 is increased will the rate of the reaction increase? Explain your answer. v) If the concentration of OCl2 is increased will the rate of the reaction increase? Explain your answer. 3. The mechanism for the catalytic decomposition of formic acid is shown below. step 1 HCOOH + H+ step 2 [HCOOHH]+ step 3 [HCO]+ → [HCOOHH]+ → → [HCO]+ CO + HOH + H+ The potential energy diagram is: 190 PE 180 170 160 150 22 Reaction Path i) The catalyst is ii) The rate determining step is iii) ΔH = iv) The reverse activation energy is v) The enthalpy of [HCOOHH]+ is vi) Is the reaction exothermic or endothermic? vii) Which chemical formula has the greatest potential energy? vii) Which chemical formula has the greatest kinetic energy? ix) Does this reaction absorb or release kinetic energy? 4. Define and remember the following definitions. Mechanism Activation energy Rate determining step Catalyst Reaction intermediate Endothermic Exothermic Activated complex ΔH Reaction rate 5. The catalyzed decomposition of acetaldehyde has an overall reaction of: CH3CHO → CH4 + CO . Determine step 2 of the reaction mechanism. A proposed mechanism is: step 1 CH3CHO + I2 → CH3I + HI + CO step 2 23 6. The following reaction has an overall reaction of: 2Ce4+ + → Tl+ 2Ce3+ + Tl3+ Determine step 2 of the reaction mechanism.A proposed mechanism is: step 1 Ce4+ + Mn+2 → Ce3+ + Mn3+ Mn4+ + Tl+ → Tl3+ + Mn2+ step 2 step 3 7. A reaction has a overall equation of: Br2 + OCl2 → BrOCl + BrCl . Determine step 3 of the mechanism. step 1 Br2 → 2Br step 2 Br + OCl2 → BrOCl + Cl step 3 List two intermediates: 8. Complete the following mechanism. step 1 NO + → Pt NO → step 2 NOPt + step 3 O2Pt → O2 overall 2NO → N2 + + Pt + O2 Identify the catalyst Identify the two intermediates 9. Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and the x axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy. 24 Fraction of collisions Collision Energy 25 Kinetics Quiz #1 1. Consider the following Reaction: HCl(aq) + NaOH(aq) → H2O(1) + NaCl (aq) The rate of this reaction could be determined by monitoring the change of concentration of : A. B. C. D. 2. 0.0013 mol/s 0.0020 mol/s 0.0030 mol/s 0.0060 mol/s Consider the following reaction: Zn(s) + 2HCl (aq) → ZnCl 2(aq) + H 2(g) Solid zinc was added to 1.0 M HCl. In 20.0 s. the temperature of the container increased by 0.05oC and 25.00 ml of H2 was produced. The rate was: A. B. C. D. 4. H+ Cl Na + H2O Consider the following reaction: 2Al (5) + 6HCl (aq) → 2AlCl 3(aq) + 3H 2(g) A 0.040 mole piece of aluminum reacted completely in 20 s. The rate of formation of hydrogen gas is : A. B. C. D. 3. Monitoring Reaction Rates 0.5oC 1.0 M HCl/s 1.25 ml H2/s 0.050 mol HCl/s Consider the following reaction: N 2(g) + 3H 2(g) → 2NH 3(g) If the rate of formulation of NH3 is 9.0 x 10–4 mol/s, then the rate of consumption of N2 is: A. B. C. D. 4.5 x 10-4 mol/s 6.0 x 10-4 mol/s 9.0 x 10-4 mol/s 1.4 x 10-3 mol/s 5. In general, the reaction rates double when the temperature is increased by 10oC . The temperature of a reaction is increased by 40oC. The rate of the reaction will be increased by: A. 2 B. 4 C. 8 D. 16 6. Consider the following reaction: 2NO2(g) → 2NO(g) + O2(g) Under certain conditions, the rate of decomposition of NO2 is 3.2 x 10-3 mol/s. The rate of the formation of O2 is: A. B. 1.6 x 10-3 mol/s 3.2 x 10-3 mol/s 26 C. D. 7. An 8.00 g piece of magnesium was placed into 6.0 M HCl . After 25 s. 3.50 g of unreacted magnesium remained. The average rate at which magnesium was consumed is: A. B. C. D. 8. 50.0 mL/80s 50.0 mL/30oC 25.0 mL/80s 25.0 mL/30oC A 25.0 mL sample of hydrogen peroxide decomposes producing 50.0 mL of oxygen gas in 137 s. The rate of formation of O2 in mL/min is A. B. C. D. 12. Mass of the system Pressure of the gas Concentration of H2O Concentration of MgCO3 At 30oC a 25.0 mL sample of bleach decomposes producing 50.0 mL of oxygen gas in 80 seconds. The rate of oxygen formation can be determined by the expression A. B. C. D. 11. grams per mole. Energy consumed per mole. volume of gas per unit time. moles formed per liter of solution Consider the following reaction at a constant temperature in an open system: MgCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + MgCl 2(aq) Which of the following properties could be used to determine reaction rate? A. B. C. D. 10. 0.14 g/s 0.18 g/s 0.32 g/s 4.50 g/s The rate of a chemical reaction can be expressed in A. B. C. D. 9. 4.8 x 10-3 mol/s 6.4 x 10-3 mol/s 0.182 mL/min 0.365 mL/min 10.9 mL/min 21.9 mL/min Consider the following reaction: 2N2O5(g) → 4 NO2(g) + 02(g) At a certain temperature the rate of decomposition of N2O5 is 2.5 x 10-6 mol/s. The rate of formation of NO2 is 27 A. B. C. D. Kinetics 1. Zn(s) + S(s) → ZnS(s) Ba2+(aq) + SO42-(aq) → BaSO4(s) NH3(g) + HCl(g) → NH4Cl(g) 2 Ag+(aq) + CO32-(aq) → Ag2CO3(s) High kinetic energy High activation energy Catalytic effect on the reaction Large surface area for the reaction Consider the following reaction: 2H2O2(aq) → 2 H2O(l) + O2(g) When 1.0 g of KI is added to the H2O2, bubbles of O2 are produced at an increased rate. When the reaction is complete, the mass of KI is 1.0 g. The KI is a A. B. C. D. 4. Factors that Change The Reaction Rate Dust particles suspended in the air inside unheated grain elevators can sometimes react explosively because the dust particles have a: A. B. C. D. 3. Quiz #2 Which of the following reactions is the slowest at room temperature? A. B. C. D. 2. 1.0 x 10-5 mol/s 1.3 x 10-6 mol/s 2.5 x 10-6 mol/s 5.0 x 10-6 mol/s Product Catalyst Reactant Reaction Intermediate Consider the following factors: I. II. III. Concentration of reactants. Temperature of reactants. Surface area of reactants. The factors that affect the rate of a chemical reaction between two gases are A. B. C. D. 5. I and II only I and III only II and III only. I, II, and III Consider the following reactions: 28 I. II. III. N2(g) + O2(g) → 2NO(g) 2Mg(s) + O2(g) → 2MgO(s) CaCO3(s) + 2H+(aq) → Ca2+(aq) + H2O(l) + CO2(g) Increasing the surface area will increase the reaction rate in A. B. C. D. 6. An untreated sugar cube does not burn when held over a lighted match. A sugar cube coated with cigarette ash readily ignites and burns. All of the cigarette ash remains after the reaction. The factor that caused this change in rate is the A. B. C. D. 7. 9. Nature of reactants Presence of a catalyst Increase in surface area Increase in concentration Which combination of factors will affect the rate of the following reaction? Zn(s) + 2HCl (aq) → ZnCl2(aq) + H2(g) A. B. C. D. 8. II only I and III only II and III only I, II and III Temperature and surfaces only Temperature and concentration only Concentration and surface area only Temperature, concentration, and surface area To increase the rate of a reaction there must be an increase in I II III IV frequency of successful collisions volume of reaction vessel pressure of the system mass of the system A. B. C. D. I only I and III only I, III and IV only I, II, III and IV Consider the following reaction: 2MnO4-(aq) + 5C2O42-(aq) + 16H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l) The rate of decomposition of the oxalate ion is increased by A. B. C. Adding NaOH Removing CO2 Adding a catalyst 29 D. 10. Which of the following factors affect the rates of both homogeneous and heterogeneous reactions I. Nature of reactants II. Presence of a catalyst III. Temperature of system IV Concentration of reactants A. B. C. D. 11. Kinetics 2. Nature of reactants Temperature of system Surface area of reactants Concentration of reactants Consider the following reaction: 2S(s) + 302(g) → 2SO3(g) + heat The rate of this reaction could be increased by A. B. C. D. 1. I and IV only II and III only. II, III and IV only I, II, III and IV Which of the following factors affects the rate of heterogeneous reactions only. A. B. C. D. 12. Decreasing the pressure. Decreasing temperature Adding a catalyst Increasing the concentration of S(s) Increasing the concentration of SO3(g) Quiz #3 Collision Theory Which of the following are necessary for successful collisions to occur? I II III Favorable collision geometry Sufficient Kinetic energy Large ∆H A. B. C. D. I only I and II only II and III only I, II, and III Collision theory states that 30 A. B. C. D. 3. A catalyst increases the rate of a reaction by A. B. C. D. 4. A decrease in surface area A decrease in ∆H for the reaction A decrease in the fraction of particles possessing sufficient energy The introduction of an alternate pathway with greater activation energy In general, a chemical reaction requiring a large activation energy will proceed A. B. C. D. 6. Increasing the concentration of the reactant(s) Decreasing the concentration of the reactant(s) Increasing the activation energy of the overall reaction Decreasing the activation energy of the overall reaction Milk is refrigerated in order to slow the rate of decomposition by bacterial action. The decrease in reaction rate is due to A. B. C. D. 5. All collisions lead to chemical reactions Most collisions lead to chemical reactions Very few reactions involve particle collisions Effective collisions lead to chemical reactions At a fast rate At a slow rate Only at a low temperature Only at low concentrations Consider the following reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) As the temperature of the above system is increased, the number of collisions A. B. C. D. 7. The minimum amount of energy needed to start a reaction is called the A. B. C. D. 8. Increases but fewer are effective Decreases and fewer are effective Increases and more are effective Decreases but more are effective Activation energy Energy of a reaction Entropy of a reaction. Reaction mechanism energy When a lit match is touched to the wick of a candle, the candle begins to burn. When the match is removed, the candle continues to burn. In this reaction, the match 31 A. B. C. D. Behaves as a catalyst Supplies activation energy Is part of the rate-determining step Lowers the activation energy barrier 32 9. Consider the following collisions, each one occurring at the same temperature Before Collision F Collision After Collision F F F Collision 1 F F N N O O N O O O O F F F F Collision 2 F F N O N O N O O O O Before Collision Collision After Collision 33 Which one of the following factors explains why collision one is successful while collision two is not successful? A. B. C. D. 10. Catalyst Geometry Concentration Kinetic energy Consider the following factors I II III IV Reactant particles collide Sufficient kinetic energy is present A favorable geometry exists Catalysts are present Which combination of the above factors is required for successful collisions A. B. C. D. 11. To increase the rate of a reaction, there must be A. B. C. D. 12. Decrease in the frequency of collisions An Increase in the frequency of collisions. A decrease in the frequency of successful collisions An increase in the frequency of successful collisions For collisions to be successful, reactants must have A. B. C. D. Kinetics 1. I only II and III only I, II, and III only I, II, III, and IV Favorable geometry only Sufficient heat of reaction only Sufficient potential energy only Sufficient kinetic energy and favorable geometry Quiz 4 Potential Energy Diagrams The addition of a catalyst to a reaction provides an alternative mechanism with A. B. C. D. Lower activation energy and lower reaction rate Lower activation energy and higher reaction rate Higher activation energy and lower reaction rate Higher activation energy and higher reaction rate 34 Consider the following Reaction: ½ N2(g) + ½ O2(g) → NO(g) ∆H = +90 kJ/mol NO The correct equation including the heat term is 2. N2(g) + O2(g) + 90 kJ → 2NO(g) N2(g) + O2(g) + 180 kJ → 2NO(g) N2(g) + O2(g) → 2NO(g) +90kJ N2(g) + O2(g) → 2NO(g) +180kJ A. B. C. D. A forward reaction has activation energy of 50 kJ and a ∆H of –100 kJ. 3. A 200 200 B 150 150 100 50 250 C D. 200 100 300 150 100 The PE diagram, which describes this reaction, is 4. Consider the following potential energy diagram 35 PE (KJ) 175 100 50 Reaction Path The Activation energy for the forward reaction is A. B. C. D. 5. Consider the following reaction: ½ H2(g) + ½ I2(g) → HI(g) The activation energy for the formation of HI is 167 kJ and for the decomposition of HI is 139 kJ. The reaction for the formation of HI is A. B. C. D. 6. 25 kJ 50 kJ 75 kJ 125 kJ Exothermic and the ∆H = -28 kJ Exothermic and the ∆H = +28 kJ Endothermic and the ∆H = -28 kJ Endothermic and the ∆H = +28 kJ Consider the following potential energy diagram 36 PE I III IV I Reaction Path The energy interval the represents the activation energy for the reverse reaction is A. B. C. D. 7. As reactant molecules approach each other A. B. C. D. 8. Heat is released A reaction intermediate forms Kinetic energy changes to potential energy Potential energy changes to kinetic Which of the following equations represents an endothermic reaction? A. B. C. D. 9. I II III IV N204(g) + 59 kJ → 2NO2(g) 2H2(g) + 02(g) → 2H2O(l) + 572 kJ 2BrCl(g) – 29.3 kJ → Br2(g) + Cl2(g) C(s) + O2(g) → CO2(g) ∆H = -394 kJ Consider the following potential energy diagram 37 2 PE 4 1 3 Progress of Reaction The interval representing ∆H for the reverse reaction is A. B. C. D. 1 2 3 4 10. Which of the following corresponds to the fastest reaction at room temperature A. Increase slowly B. Remain constant C. Decrease slowly D. Increase rapidly due to alternate pathway 12. Consider the following potential energy diagram that represents two different reactions. Which of the following statements is correct? A A. B. C. D. B Reactions A and B are both exothermic Reactions A and B are both endothermic Reaction A is exothermic and reaction B is endothermic Reaction A in endothermic and reaction B is exothermic 38 13. Consider the following reaction: ½ H2(g) + ½ I2(g) → HI(g) ∆H = +28 kJ The activation energy for the formation of HI is 167 kJ. the activation energy for the decomposition of HI is: A. B. C. D. Kinetics 1. 28 kJ 139 kJ 167 kJ 195 kJ Quiz #5 Mechanisms Consider the following reaction mechanism Step 1: M + X → MX Step 2: MX + A → D + X The chemical species MX is a(n) A. B. C. D. 2. Catalyst Inhibitor Final Product Reaction Intermediate Consider the following reaction mechanism Step 1: NO2 + NO2 → NO + NO3 Step 2: NO3 + CO → NO2 + CO2 The overall reaction is A. B. C. D. 3. 2NO2 → NO3 + NO NO2 + CO → NO + CO2 NO3 + CO → NO2 + CO2 NO2 + NO3 + CO → NO3 + NO2 + NO + CO2 Consider the following reaction mechanism Step 1: Step 2: V3+ + Cu2+ → V4+ + Cu+ Cu+ + Fe3+ → Cu2+ + Fe2+ (slow) (fast) The reaction intermediate is A. B. C. D. 4. Cu+ Cu2+ V3+ Fe3+ Consider the following reaction Mechanism 39 Step 1: H2O2 + I - → H2O + IOStep 2: H2O2 + IO - → H2O + O2 + I The reaction intermediate is A. B. C. D. 5. IIO H2O H2O2 Consider the following potential energy diagram PE (kJ) Progress of the reaction The above potential energy diagram represents an A. B. C. D. Exothermic reaction involving one step Exothermic reaction involving two steps Endothermic reaction involving one step Endothermic reaction involving two steps 40 6. Consider the following reaction mechanism Step 1: NO2(g) + NO2(g) → NO(g) + NO3(g) (slow) Step 2: NO3(g) + CO(g) → CO2(g) + NO2(g) (fast) Which one of the following changes would result in the greatest increase in reaction rate A. B. C. D. 7. Increase [CO] Decrease [NO] Increase [NO2] Increase [NO3] An uncatalyzed reaction was found to produce 40 kJ of energy in 10 mins. When catalyzed, the same reaction produced 40 kJ of energy in 2 mins. Which one of the following potential energy diagrams is consistent with the above data? PE A B PE Reaction Path C PE Reaction Path D Reaction Path 8. PE Reaction Path Consider the following reaction mechanism Step 1: ICl + H2 → HI + HCl (slow) Step 2: ICl + HI → HCl + I2 (fast) The Species HCl is a 41 A. B. C. D. 9. Product Catalyst Reactant Reaction Intermediate Consider the following reaction mechanism Step 1: Cl(g) + O3(g) → ClO(g) + O2(g) Step 2: O(g) + ClO(g) → Cl(g) + O2(g) The Reaction intermediate is A. B. C. D. 10. Cl O2 O3 ClO In a reaction mechanism, the rate determining step is the A. B. C. D. Fastest and has the lowest reaction rate. Fastest and has the highest activation energy Slowest and has the lowest activation energy Slowest and has the highest activation energy PE Reaction Progress 11. Select the true statement concerning the above potential energy diagram. A. B. C. D. The catalyzed reaction has a larger ∆H The uncatalyzed reaction has a larger ∆H The catalyzed reaction has a greater rate of reaction The uncatalyzed reaction has a greater rate of reaction 42 I II 12. O2 O3 NO NO2 Consider the following reaction mechanism Step 1: N2O(g) → N2(g) + O(g) Step 2: N2O(g) + O(g) → N2(g) + O2(g) The reactant in the overall reaction is A. B. C. D. 15. I II III IV Consider the following reaction Step 1: NO(g) + O3(g) → NO2(g) + O2(g) Step 2: O(g) + NO2(g) → NO(g) + O2(g) The catalyst is A. B. C. D. 14. IV Which point on the diagram above represents the potential energy of the activated complex formed in the uncatalyzed reaction? A. B. C. D. 13. III O O2 N2 N2O Consider the following reaction O3(g) + NO(g) ----- > NO2(g) + O2(g) NO2(g) + O(g) ------ > NO(g) + O2(g) The product in the overall reaction is A. B. C. D. O2 O3 NO NO2 43 Kinetics 1. Web Review Define the following: Activation energy, Mechanism Activated Complex Successful collision Catalyst Reaction rate Enthalpy Intermediate Homogeneous reaction Rate determining step Heterogeneous reaction. 2. 3. Na2CO3(aq) + 2HCl(aq) → CO2(g) + 2NaCl(aq) +H2O(l) a) Give four ways to increase the rate of the reaction. b) Give three properties that you could measure in order to determine the rate experiment. Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq) 44 a) Give five specific ways to increase the rate. 4. In low light, H2 and Cl2 do not react at all. When exposed to UV light, they react explosively! Explain using the collision theory. 5. A mixture of KClO3 and C12H12O11 do not react at all at room temperature. A drop of H2SO4 starts the reaction, slowly at first, then it quickens into a flaming inferno. Explain using the collision theory. 6. Water puts out a fire. Explain using the collision theory. 7. A glowing splint re-ignites in pure O2. Explain using the collision theory. 8. Enzymes in the human body allow the oxidation of carbohydrates at 37 degrees Celsius. 9. Draw an exothermic PE diagram. Include a catalyst. Label the change in enthalpy, the forward and reverse activation energies and the activated complex. 45 10. Repeat the above for an endothermic reaction. 11. A student reacts CaCO3(aq) with excess HCl in an open container at a constant temperature. The equation for the reaction is: CaCO3(s) + 2HCl(aq) → CO2(g) + CaCl2(aq) + H2O(l) In terms of the collision theory, describe what will happen to the rate of the reaction as the reaction proceeds from the beginning to completion. Hint: what happens to the [HCl] as the reaction proceeds and what effect would that have on the rate. 12. A + WY → AWY Fast AWY + HA → A2WY + H Slow A3 + WY + H Fast A2WY + HA → For the above reaction mechanism list the following: a) The overall equation b) A catalyst c) Intermediates d) Reactants 46 e) Products Describe how each change affects the rate. 13. a) Increasing the concentration of A b) Increasing the concentration of H c) Increasing the concentration of HA d) Removing WY completely e) Decreasing the temperature Describe the KE and PE changes as two molecules: a) Approach to collide, b) Form an activated complex, and c) Form products in an exothermic reaction. 14. Draw the PE diagram for a mechanism with three steps. How many activated complexes are there? How many intermediates are there? 15. Describe as endothermic or exothermic. a) 2H2 + O2 → 2H2O + 300kJ b) NH4NO3(s) → NH4NO3(aq) ΔH = +150kJ 16. Change each equation in 15 from standard to ΔH notation or vice-versa. 17. Which reaction at room temperature is faster and why? a) Pb2+ + 2Cl- → b) 2H2 + O2 → PbCl2 or 2H2O 18. List three commercial catalysts (they are in your textbook) 19. Calculate the rate in moles/s. Moles H2 10.0 15.0 21.0 24.0 Time (seconds) 200 300 400 500 47 20. Indicate how each change will affect the rate of the reaction and the PE diagram and explain with the collision theory. a) Increasing the temperature b) Increasing the concentration of a reactant c) Increasing the concentration of a product b) Addition of a catalyst X + Y → XY 21. slow XY + Z → XYZ fast XYZ + W → XYW + Z fast a) Identify intermediates, the catalyst and the rate-determining step. b) If the concentration of X was increased will the rate increase? 22. You can only increase the surface area of a substance if it is in certain physical state. What is it? 23. Two solid reactants react. Is it a homogeneous or heterogeneous reaction? 24. What is the mathematical relationship between each of the following? Reaction rate and activation energy Reaction rate and reactant concentration Reaction rate and temperature 25. Draw a collision energy distribution diagram for a reaction where the y axis is fraction of collisions and the x axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy. 48 Faction of collisions Collision Energy 26. Shade in the area of the collision energy distribution diagram showing those collisions that do not have the required energy to be successful at the temperature below. Faction of collisions Collision Energy 49 Practice Test # 1 1. 2. Consider the following reaction mechanism: step 1: M + X → step 2: MX + A → The chemical species MX is a(n) A. catalyst B. inhibitor C. final product D. reaction intermediate 1.0 1.3 2.5 5.0 A. B. C. D. x x x x 10-5 mol/s 10-6 mol/s 10-6 mol/s 10-6 mol/s nature of the reactants presence of a catalyst temperature of system concentration of reactants I and IV only II and III only II, III, and IV only I, II, III, and IV Which of the following equations represents an endothermic reaction? A. B. C. D. 5. X Which of the following factors affect the rates of both homogeneous and heterogeneous reactions. I II III IV 4. + Consider the following reaction: 2N2O5(g) → 4NO2(g) + O2(g) At a certain temperature the rate of decomposition of N2O5(g) is 2.5 x 10-6 mol/s. The rate of formation of NO2 is A. B. C. D. 3. MX D N2O4(g) 2H2(g) 2BrCl(g) 2H2(g) + 59 kJ → 2NO2(g) + O2(g) → 2H2O(l) + 572 kJ -29.3 kJ →Br2(g) + Cl2(g) + O2(g) → 2H2O(l) ΔH = -572 kJ Consider the potential energy diagram. The activation energy for the reverse reaction is 50 PE (kJ) 170kJ 30kJ Progress of the reaction A. B. C. D. 6. Consider the following mechanism: Step 1: Step 2: The reaction intermediate is A. B. C. D. 7. + O2 + O2 Cl O2 O3 ClO fastest and has the lowest activation rate. fastest and has the highest activation rate. slowest and has the lowest activation rate. slowest and has the highest activation rate. A catalyst increases the rate of a reaction by A. B. C. D. 9. Cl + O3 → ClO O + ClO → Cl In a reaction mechanism, the rate determining step is the A. B. C. D. 8. 30 kJ 140 kJ 170 kJ 200 kJ increasing the concentration of reactant(s). decreasing the concentration of the reactant(s). increasing the activation energy of the overall reaction. decreasing the activation energy of the overall reaction. Which of the following properties could be used to measure the rate of the following reaction in a open container. Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) A. B. C. D. mass of Zn solubility of HCl concentration of Clcolour of the solution 51 10. Consider the following potential energy diagram: PE (kJ) Progress of the reaction The above diagram represents an A. B. C. D. 11. exothermic reaction involving one step. exothermic reaction involving two steps. endothermic reaction involving one step. endothermic reaction involving two steps. Which of the following are necessary for successful collisions to occur? I. II. III. A. B. C. D. 12. Favourable geometry Sufficient energy Large ΔH I only I and II only II and III only I, II, and III Consider the following reaction: 2H2O2(aq) → 2H2O(l) + O2(g) When 1.0 g of KI is added to the H2O2, bubbles of O2 are produced at an increased rate, The KI is a A. B. C. D. product catalyst reactant intermediate 52 13. Consider the following I. Frequency of successful collision II. Volume of the reaction vessel III. Pressure of the system IV Mass of the system To increase the rate of a chemical reaction there must be an increase in A. B. C. D. 14. I only I and III only I, III and IV only I, II, III, and IV Consider the following reaction mechanism: Step1: ICl + H2 → HI + HCl slow Step 2: ICl + HI → HCl + I2 fast The species HCl is a A. B. C. D. 15. product catalyst reactant reaction intermediate Consider the following potential energy diagram: 125 PE (kJ) 100 50 25 Progress of the reaction 53 The activation energy in the forward direction is A. B. C. D. 16. Consider the following reactions: I. N2 + O2(g) → 2NO(g) II. Mg(s) + O2(g) → 2MgO(s) III. CaCO3(s) + 2H+(aq) → Ca2+ (aq) + H2O(l) + CO2(g) Increasing the surface area will increase the reaction rate in A. B. C. D. 17. 25 kJ 50 kJ 100 kJ 125 kJ II only I and III only II and III only I, II, and III Consider the following reaction mechanism: Step 1: V3+ + Cu2+ → V4+ + Cu+ Step 2: Cu+ + Fe3+→ Cu2+ + Fe2+ slow The reaction intermediate is A. B. C. D. 18. The rate of a chemical reaction can be expressed in A. B. C. D. 19. grams per mole energy consumed per mole volume of gas per unit time mole formed per litre of solution Consider the following reaction: 2MnO4-(aq) + 5C2O42-(aq) 16H+(aq) → 2Mn2+(aq) + 10CO2(g) + 8H2O(l) The rate of decomposition of the oxalate ion is increased by A. B. C. D. 20. Cu+ Cu2+ V3+ Fe3+ adding NaOH. removing CO2 adding a catalyst decreasing the pressure The minimum amount of energy needed to start a reaction is called the 54 A. B. C. D. 21. An 8.00 g piece of magnesium was placed into 6.0 M HCl. After 25 s, 3.50 g of unreacted magnesium remained. The average rate at which magnesium was consumed is A. B. C. D. 22. 0.14 g/s 0.18 g/s 0.32 g/s 4.50 g/s In general rates double when the temperature is increased by 10 oC. The temperature of a reaction is increased by 40 oC. The rate will increase by a factor of A. B. C. D. 23. activation energy. energy of reaction. entropy of reaction reaction mechanism energy 2 4 8 16 Consider the following factors I. reactant particles collide II. sufficient kinetic energy is present III. a favourable geometry exists IV. catalysts are present Which combination of the above factors is required for all successful collisions? A. B. C. D. 24. Consider the following reaction at constant temperature in an open system: MgCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + MgCl2(aq) Which of the following properties could be used to determine the reaction rate. A. B. C. D. 25. I only II and III only I, II and III only I, II, III, and IV mass of the system pressure of the gas concentration of H2O concentration of MgCO3 Which combination of factors will affect the rate of the following reaction? MgCO3(s) + 2HCl(aq) → CO2(g) + H2O(l) + MgCl2(aq) A. temperature and surface area only B. temperature and concentration only C. concentration and surface area only D. temperature, concentration, and surface area only 55 26. As reactant molecules approach each other A. B. C. D. heat is released a reaction intermediate forms kinetic energy changes into potential energy potential energy changes into kinetic energy Consider the following potential energy diagram for the next five questions. 2 PE 4 1 3 Progress of reaction 27. The interval representing ΔH for the reverse reaction is A. B. C. D. 28. The interval representing ΔH for the forward reaction is A. B. C. D. 29. 1 2 3 4 The interval representing Ea for the forward reaction is A. B. C. D. 31. 1 2 3 4 The interval representing Ea for the reverse reaction is A. B. C. D. 30. 1 2 3 4 1 2 3 4 The interval representing the energy of the activated complex is 56 A. B. C. D. 32. When a catalyst is added to a reaction, ΔH will A. B. C. D. 33. 1 2 3 4 increase slowly remain constant decrease slowly increase rapidly due to the alternate pathway Consider the following reaction: Zn(s) + 2HCl(aq) → H2(g) + ZnCl2(aq) Data for the reaction is shown below: Time 0 2 4 Mass of Zn (g) Volume of H2 (mL) Temperature (oC) 4.65 4.50 4.35 0 50 100 20 21 22 The rate of the reaction can be measured in units of A. B. C. D. 34. When a lit match is touched to the wick of a candle, the candle begins to burn. When the match is removed, the candle continues to burn, the match, A. B. C. D. 35. behaves as a catalyst supplies the activation energy is part of the rate determining step lowers the activation energy barrier Consider the following reaction: 2NO(g) + O2(g) → 2NO2(g) + 112 kJ ΔH for the above reaction is: A. B. C. D. 36. g/min g/mL min/mL g/(mL)(oC) positive and the reaction is exothermic negative and the reaction is exothermic positive and the reaction is endothermic negative and the reaction is endothermic Consider the following reaction: 2S(s) + 3O2(g) → 2SO2(g) + heat The rate of this reaction could be increased by 57 A. B. C. D. 37. Consider the following reaction: ½H2 + ½I2 → HI ΔH = +28 kJ The activation energy for the formation of HI is 167 kJ. The activation energy for the decomposition of HI is A. B. C. D. 38. A. decreasing the temperature adding a catalyst increasing the concentration of S decreasing the surface area of the S 28 kJ 139 kJ 167 kJ 195 kJ Some reactants are more reactive than others because of their activation energy Ea. What graph shows the relationship between Ea and rate. B. Ea Ea Rate C. Rate D. Ea Rate 39. Rate The activated complex is a chemical species that is A. B. C. D. 40. Ea stable and has low PE. stable and has high PE. unstable and has low PE. unstable and has high PE. As an activated complex changes into products, A. B. C. D. potential energy changes into kinetic energy. kinetic energy changes into potential energy. kinetic energy changes into activation energy. potential energy changes into activation energy. 58 Subjective PE Progress of the reaction 1. On the potential energy diagram above, clearly label the activation energy, heat of the reaction (∆H), and the energy of the activated complex. 2. Is the above reaction endothermic or exothermic in the forward direction? 3. On the graph below, draw the potential energy diagram for an exothermic reaction and label the activation energy. PE Progress of the reaction 4. a) Nitric oxide (NO) is involved in the decomposition of ozone by the following mechanism: Step 1: O3 + sunlight → O2 + O Step 2: O3 + NO → NO2 + O2 Step 3: NO2 + O → NO + O2 Write the net equation for the decomposition reaction 59 b) Identify a catalyst c) Identify a reaction intermediate d) What is the function of sunlight in this reaction? 5. Consider the following reaction: a) Explain why the reaction is likely to involve more than one step. b) A proposed mechanism for the above reaction is: Step 1: NO + H2 → N + H2O Step 2: ? Step 3: N2O + H2 → N2 + H2O 2NO + 2H2 → 2H2O + N2 Write the equation for step 2. 6. Define the term activation energy. 7. The combustion of coal, C, produces carbon dioxide and water according to the following equation: C(s) + O2(g) → CO2(g) + 394 kJ a) What is ∆H for this reaction? b) Using the collision theory, explain why a lump of coal does not react with oxygen at room temperature and pressure. c) Many coalmine disasters have resulted when a spark ignites coal dust in the air. Explain using the collision theory. 8. State two reasons why some collisions may not result in a chemical reaction. 9. A student wishes to monitor the rate of the following reaction: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) 60 Identify two different properties that could be used to monitor the rate of the reaction. Describe and explain the changes that would occur. Property 1 Change and explanation Property 2 Change and explanation 10. An experiment is done to determine the rate of the following reaction: 2Al(s) + 6HCl(aq) → 3H2(g) + 2AlCl3(aq) Balance 1.00 g of Al is placed in a beaker and allowed to react for 12.00 minutes with 2.00 M HCl. If the rate of consumption of HCl is 0.250 g/min, calculate the amount of Al remaining. 61 Kinetics Practice Test # 2 1. Which of the following units could be used to express the reaction rate? A. B. C. D. 2. Consider the reaction: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) The rate of production of ZnCl2, can be increased by A. B. C. D. 3. potential energy changes to kinetic energy. kinetic energy changes to potential energy. kinetic energy changes to activation energy. potential energy changes to activation energy. Which of the following is most likely to have the greatest rate at room temperature. A. B. C. D. 6 enthalpy. activation energy. the ΔH of the reaction. the activated complex. As an activated complex changes to products, A. B. C D. 5. decreasing the [HCl]. increasing the temperature increasing the volume of H2. decreasing the surface area of Zn. The statement, the minimum energy needed for a successful collision, defines A. B. C. D. 4. mL/s mL/g g/mL mL/mol 2H2(g) + O2(g) → 2H2O(l) 2Ag+(aq) + CrO42-(aq) → Ag2CrO4(s) Pb(s) + 2HCl(aq) → PbCl2(aq) + H2(g) CH4(g) + 2O2(g) → CO2(g) + H2O(g) Consider the following PE diagram for an uncatalyzed and catalyzed reaction 62 PE (kJ) 35kJ 10kJ 15kJ Progress of the Reaction Which of the following describes the forward catalyzed reaction? Activation Energy (kJ) A. B. C. D. 7. product catalyst reactant intermediate Activation energy can be described as the A. B. C. D. 9. -15 15 -15 15 A substance that increases the rate of a reaction without appearing in the equation for the overall reaction is a(an) A. B. C. D. 8. 10 10 25 25 ΔH (kJ) energy of motion energy of the activated complex. energy difference between the reactants and the products. energy difference between the reactants and the activated complex. What effect does a catalyst have on a reaction? A. B. C. D. It changes the ΔH of a reaction. It increases the kinetic energy of the reactants. It decreases the potential energy of the products. It provides a reaction mechanism with a lower activation energy. 63 10. Consider the following reaction involving 1.0 g of powdered zinc: Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) Trial Temperature (0C) Concentration of HCl 1 2 3 40 20 40 3.0 3.0 6.0 The rates in order of fastest to slowest are A. B. C. D. 11. 1, 2, 3 2, 1, 3 3, 1, 2 3, 2, 1 Consider the following potential energy diagram for a reversible reaction: 140 130 PE (kJ) 110 Progress of the reaction Which of the following describes the system above? A. B. C. D. 12. Activation Energy (kJ) ΔH (kJ) reverse reverse forward forward 10 10 30 20 -20 -30 +10 +30 An activated complex is a chemical species that is A. B. C. D. 13. Reaction stable and has low PE. stable and has high PE. unstable and has low PE. unstable and has high PE. Consider the reaction: Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g) 64 At a certain temperature, 2.05 g Ca reacts completely in 30.0 seconds. The rate of consumption of Ca is A. B. C. D. 14. 15. 0.00208 mol/min 0.0833 mol/min 0.102 mol/min 5.00 mol/min Increasing the temperature of a reaction increases the reaction rate by I. II. III. increasing frequency of collision increasing the kinetic energy of collision decreasing the potential energy of the collision A. B. C. D. I only. I and II only. II and III only. I, II, and III. A certain reaction is able to proceed by various mechanisms. Each mechanism has a different Ea and results in a different overall rate. Which of the following best describes the relationship between the Ea values and the rates? A. B. Ea Ea Rate C. Rate D. Ea Rate Ea Rate 65 16. For collisions to be successful, reactants must have A. B C. D. 17. favourable geometry. sufficient heat of reaction only. sufficient potential energy only. sufficient kinetic energy and favourable geometry. Consider the following reaction: 1/2 H2(g) + 1/2 I2(g) → HI(g) ΔH = +28 kJ The activation energy for the formation of HI is 167 kJ. The activation energy for the decomposition of HI is A. B. C. D. 18. 28 kJ 139 kJ 167 kJ 195 kJ Which of the following factors affects the rate of heterogeneous reactions only? A. B. C. D. nature of the reactant temperature surface area of reactants concentration of reactants 19. A 25.0 mL sample of hydrogen peroxide decomposes producing 50.0 mL of oxygen gas in 137 s. The rate of formation of O2 in mL/min is A. B. C. D. 20. 0.182 mL/min 0.365 mL/min 10.9 mL/min 21.9 mL/min Consider the following reaction mechanism: step 1 step 2 2NO + H2 → N2 + H2O2 H2O2 + H2 → 2H2O In this reaction H2 is a A. B. C. D. product catalyst reactant reaction intermediate 66 21. Which of the following properties could be used to measure the rate of the following reaction taking place in an open container? Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) A. B. C. D. 22. mass of Zn solubility of HCl concentration of Clcolour of the solution Consider the following reaction: N2 + 3H2 → 2NH3 The rate of formation of NH3 is 3.0 mole/min. The rate of consumption of H2 is: A. B. C. D. 23. 1.5 mole/min 2.0 mole/min 4.5 mole/min 9.0 mole/min Consider the following reaction mechanism: NO2 + NO2 → N2O4 N2O4 + CO → CO2 + NO + NO2 Step 1 Step 2 In the overall reaction, N2O4 is a A. B. C. D. 24. product catalyst reactant reaction intermediate Consider the following mechanism: NO + O3 → NO2 + O2 O + NO2 → NO + O2 Step 1 Step 2 The catalyst is A. B. C. D. O2 O3 NO NO2 67 25. Consider the following reaction: Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) The rate of this reaction increases when more Mg is added. This change is caused by the A. B. C. D. 26. addition of a catalyst increase in surface area change in the nature of the reactants increase in concentration of reactants Consider the following PE diagram 100 PE (kJ) 40 20 Progress of the reaction The forward reaction can be described as A. B. C. D. 27. ΔH Ea Type +20 +20 -20 -20 80 60 80 100 endothermic exothermic exothermic endothermic Consider the following reaction: HgO(s) → Hg(l) + 1/2O2(g) The rate of this reaction can be expressed as A. B. C. D. rate rate rate rate = = = = [O2]1/2 Δ[O2]/Δt Δ[Hg]/Δt Δ[HgO]/Δt 68 28. Which of the following would react most rapidly? A. B. C. D. 29. Addition of a catalyst to a reaction increases the rate because it A. B. C. D. 30. Powdered Zn in 1.0 M HCl at 25 0C Powdered Zn in 2.0 M HCl at 40 0C A lump of Zn in 2.0 M HCl at 25 0C A lump of Zn in 1.0 M HCl at 40 0C increases the value of ΔH decreases the value of ΔH provides an alternate mechanism with a lower Ea provides an alternate mechanism with a higher Ea When a collision occurs between two reactant species which possess between them the minimum kinetic energy a product does not always form. This may be a result of A. B. C. D. low temperature small surface area low concentrations unfavourable geometry Subjective Section 1. An experiment is done to determine the rate of the following reaction; 2Al(s) + 6HCl(aq) → 3H2(g) + 2AlCl3(aq) H2 The following data are collected: Time (s) Mass of Beaker + Contents (g) 270.170 g 0.0 30.0 60.0 270.230 270.200 270.170 Calculate the rate of consumption of Al in moles/min 2. 3. Define the term activation energy. Define the word Activated complex. 4. Define the word mechanism. 69 5. Consider the following reaction mechanism Step 1 6. ? Step 2 H2 + Cl → HCl + H Step 3 H + Cl2 → HCl + Cl Step 4 Cl + Cl → Cl2 Overall H2 + Cl2 → 2HCl a) Write the equation for step 1 b) Identify the reaction intermediate(s) Consider the overall reaction: 4HBr + O2 → 2H2O + 2Br2 A proposed three-step mechanism is: Step 1 HBr + O2 → HOOBr Step 2 ? Step 3 HBr + HOBr → H2O + Br2 Write the equation for step 2. 7. A student wishes to monitor the rate of the following reaction: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) Identify two properties that could be used to monitor the rate of the reaction. Describe and explain the changes that would occur. Property 1 Change and explanation 70 Property 2 Change and explanation 8. Carbon burns in air according to the following equation: C(s) + O2(g) → CO2(g) List four ways the rate of the above reaction could be increased. 9. Sketch the potential energy diagram for an endothermic reaction in the space below. On your diagram clearly label: PE Progress of the Reaction i) ii) iii) the energy of the activated complex the activation energy ΔH 71 Kinetics Worksheets for Chemistry 12 Mr. Iannone Notes- double click on the lesson number and download Power Point Viewer if you do not have it. Worksheets Quiz Q1 Q2 Q3 Q4 Q5 1 2 3 4 5 Monitoring Reaction Rates Factors that Change the Rate Collision Theory PE Diagrams Mechanisms WS 1 WS 2 WS 3 WS 4 WS5 6 7 Lab: The Iodine Clock Reaction Review 8. 9. Review Test Web Review Practice Test 1 Practice Test 2 Quizmebc Text book Hebden Read Unit I The following workbook is designed to ensure that you can demonstrate your understanding of all aspects of the kinetics unit. The minimum expectation is that you do all of these questions by the due dates given by your teacher. Do the questions. Use your notes from class to assist you. Then after you have finished go to the web site to evaluate your work. Make a list of those things that you don’t quite understand and bring them to class. I will go over them as best as I can. There are other things that you should do to prepare for the test at the end of the unit. Remember, what you put into this course is what you will get out. There is no substitute for consistent effort and hard work. If you can’t do a question, get some help before the end of the unit, you need to know, understand, and remember everything. Good luck! I know you can do well in this unit. Web Site Address: sd34.bc.ca/schools/wjm/science/chem12 Ws #1 Monitoring and Calculating Reaction Rates 1. Read unit 1 of Hebden over the next week. “A” students should read it twice. 2. a) When measuring a property associated with a reactant in a reaction, does it increase or decrease? Decrease as reactants are converted into products 72 2. b) When measuring a property associated with a product in a reaction, does it increase or decrease? Increase as reactants are converted into products 3. Give three ways to measure the rate of the following reaction. State the specific properties that you would monitor and include units (amount is not a specific property). State if each property would increase or decrease. Describe in each case how you would calculate the reaction rate. 2HNO3(aq) + Cu(s) → NO2(g) +H2O(l) + CuNO3(aq) The first one is done for you. i) Mass of Cu mass/time ii) [HNO3] M/time iii) Volume of NO2 L/time iv) [CuNO3] M/time v) Mass of open container mass/time vi) Pressure of closed container Pressure/time Grams Decrease Rate = M Decrease Rate = L Increase Rate = M increase Rate = Grams Decrease Rate = KPa Increase Rate = Any three of the above answers are fine. Mass of copper (g) Time (min) 3.26 5.0 2.93 7.0 2.61 9.0 4. Calculate the rate in units of (g Cu/min). 3.26 - 2.61 g Cu = 0.16g/min 9.0 - 5.0 min 5. Calculate the rate in units of (mole Cu/min). 0. 16g Cu x 1 mol = 0.0026 mol/min min 63.5 g 6. Calculate the rate in moles HNO3 consumed per second (remember that 2 moles are consumed per 1 mole of Cu). 0.0026 mol Cu x 1 min x 2 moles HNO3 = 8.5 x 10-5 moles/s min 60s 1 mole Cu 7. Calculate the rate in units of (g/sec) for HNO3. 8.5 x 10-5 moles HNO3 x 63.0 g = 0.0054 g/s s 1 mole Volume of NO2 (mL) 10.0 11.5 12.7 73 Time (sec) 0.00 5.00 10.00 8. Calculate the rate in units of (mL NO2/sec). Rate = 12.7 - 10.0 ml = 0.27 ml/s 10.00 - 0.00 s 9. Calculate the rate in units of (L NO2/min). 0.27 ml x 60s x 1L = 0.016 L/min s 1 min 1000 ml 10. Calculate the rate in units of (moles NO2/min) at STP. 0.0162 L x 1 mol = 7.2 x 10-4 mol/min min 22.4 L 11. Calculate the rate in units of (moles HNO3/min) at STP (remember that 2 moles are consumed per 1 mole of NO2) 7.23 x 10-4 mol NO2 x 2 moles HNO3 = 0.0015 moles/min min 1 mole NO2 12. Calculate the rate of the following reaction: 2NO (g) + 2H2 (g) → N2 (g) + 2H2O (g) moles NO Time(s) 0.080 0.060 0.040 0.020 0.0 2.0 4.0 6.0 8.0 10.0 11.0 12.0 74 Rate = (0.080 – 0.020) moles = 0.0060 moles/s (12.0 – 2.0) s a) What is the rate in moles NO per second? 0.0060 moles/s b) What is the rate in moles N2 per second? 0.0030 moles/s c) What is the rate in grams NO per min? 11 g/min d) What is the rate in grams N2 per hour? 3.0 x 102g/h 13. Choose three properties that you could measure in order to monitor the rate of the following reaction. Cu (s) + 2AgNO3 (aq) → 2 Ag (s) + Cu(NO3)2 (aq) Property Unit of Measurement Change 1. Mass Cu grams decrease 2. Mass Ag grams increase 3. Intensity [Cu+2] M increase 14. Calculate the rate of the following reaction in units of M/s: Zn (s) + 2HCL (aq) → ZnCl2 (aq) Molarity of HCL (M) time (seconds) 0.612 21.0 Rate = (1.05 - 0.612) M (29.0 - 21.0) s = + H2 (g) 0.813 25.0 1.05 29.0 0.055 M/s 15. Calculate the rate of the following reaction in L/min: Zn (s) + 2HCL (aq) → ZnCl2 (aq) + H2 (g) Volume of H2 (L) 0.255 0.550 0.790 time (minutes) 1.0 2.0 3.0 75 Rate = (0.790 - 0.255) M (3.0 - 1.0) s = 0.27 L/min 16. If 0.369g of HCl is neutralized with 0.250M NaOH in 25.0 seconds, what is the reaction rate in moles HCL /min. Rate = WS # 2 0.369g x 1 mole 36.5g 0.41666 min = 0.0243 mole/min Factors That Change The Reaction Rate Homogeneous reactions - reactants are in the same phase (aq), (g) , or (l) and are thoroughly mixed. Heterogeneous reactions - reactants are in the two or more phases and are not thoroughly mixed (two solids do not mix). Classify as Homogeneous or Heterogeneous: 1. Zn (s) + 2 HCl (aq) → H2 (g) + ZnCl2 2. Ag+ (aq) + Cl- (aq) → AgCl 3. H2 (g) + F2 (g) 4. 2Al (s) + 3I2 (s) → → (s) (aq) heterogeneous homogeneous 2HF (g) homogeneous 2AlI3 heterogeneous (s) The following four factors will increase the rate of a chemical reaction that is homogeneous: 1. Increasing the temperature. 2. 3. 4. 5. Increasing the reactant concentration. Adding a catalyst Changing the nature of the reaction. Increasing the pressure for gases The above four factors as well as the two below will increase the rate of a heterogeneous reaction: 6. 7. Increasing the surface area of a solid. Agitation 76 Which factor will only increase the rate of a gaseous reaction? 8. Pressure For each reaction specifically describe all of the ways to increase the reaction rate (i.e.. increase[H2]). 1. H2 (g) + F2 (g) → 2 HF (g) This reaction is homogeneous so the first four factors will work. Increasing the temperature Increasing the pressure Increasing [H2] or [F2] Adding a catalyst 2. HCl (aq) + NaOH (aq) → NaCl (aq) + H2O factors will work. (l) This reaction is homogeneous so the first four (aq) This reaction is heterogeneous most of the factors Increasing the temperature Increasing [HCl] or [NaOH] Adding a catalyst 3. Zn (s) + 2 HCl (aq) → H2 (g) + ZnCl2 will work, except pressure- need a gaseous reactant.. Increasing the temperature Increasing [HCl] Adding a catalyst Increasing the surface area of Zn(s) Agitation 4. State three examples of chemical reactions that are desired to be slow. Food spoiling Metal corrosion Erosion 5. Give three examples of chemical reactions that are desired to be fast. Combustion of gasoline in automobiles Industrial chemical production Cooking food The combustion of gasoline in a car engine; while accelerating. 77 6. List all of the ways to increase the rate of the following reaction: H2O2 (aq) → H2 (g) + O2 (g) Increasing the temperature Increasing [H2O2] Adding a catalyst I. Homogeneous reactions are generally faster than heterogeneous- the reactants are mixed better and therefore there are more collisions between reactant particles. HCl (aq) + NaOH (aq) → is NaCl (aq) + H2O (l) faster than → H2 (g) + ZnCl2 Zn (s) + 2 HCl (aq) (aq) II. Simple ionic reactions (where there are no bonds to break) are generally faster than more complex ionic reactions (where there are bonds to break). Pb+2 (aq) + 2Cl- (aq) is 2Na+ (aq) + 2ClO- (aq) → → PbCl2 (l) faster than 2Na+ (aq) + 2Cl-(aq) + O2 (g) 1. Indicate the faster and slower reaction and explain why. a) 2Al (s) + 3I2 (s) → 2AlI3 (s) Heterogeneous reaction with bonds to break will be slow. b) Ag+(aq) + Cl-(aq) → AgCl (s) Homogeneous reaction with no bonds to break will be fast. 2. Indicate the faster and slower reaction and explain why. a) 2Al (s) + 3I2 (s) → 2AlI3 (s) Slow. The reaction is heterogeneous (two solid do not mix) with bonds to break. b) 2Na+ (aq) + 2ClO- (aq) → 2Na+ (aq) + 2Cl-(aq) + O2 (g) Faster. The reaction is homogeneous. 78 3. Indicate the faster and slower reaction and explain why. a) 3Ba+2(aq) + 2PO4-3 (aq) → Ba3(PO4)2(aq) Faster. The reaction is homogeneous and simple ionic with no bonds to break. b) Cu(s) + 2Ag+(aq) → Cu+2 (aq) + 2Ag (s) Slow. The reaction is heterogeneous and the Cu(s) bonds need to be broken. Ws # 3 Collision Theory 1. 2. Chemical reactions are the result of collisions between reactant particles, where bonds are broken and new ones form. A successful collision requires sufficient energy and favorable geometry. 3. Describe as fast, medium or slow. Explain! i) 2 H2 (g) + O2 (g) → 2 H20 (l) (room temperature) Slow. Gas reactions are slower than aqueous. ii) 2 Ag+ (aq) + CO32- (aq) → Ag2CO3 (s) Fast. Homogeneous reaction simple ionic- there are no bonds to break iii) 2 HCl (aq) + Na2CO3 (aq) → CO2 (g) + 2 NaCl (aq) + H20 (l) Medium. Homogeneous complex reaction - there are bonds to break. 4. i) Describe how you would measure the rate of the reaction : Zn (s) + 2 HCl (aq) → ZnCl2 (aq) + H2 (g) Measure the decrease in Zn mass. Measure the increase in H2 gas volume. Measure the mass of an open container which decreasing due H2 escaping. ii) List four ways to increase the rate. Increasing the temperature Increasing [HCl] 79 Adding a catalyst Increasing the surface area of Zn(s) Agitation 5. A 10 °C temperature increase frequently doubles the rate of a slow reaction because: a) The temperature has doubled. b) The PE of the colliding particle has doubled. c) The KE of the colliding particle has doubled. d) The fraction of particles with sufficient KE to react has doubled. 6. Both collisions A and B have the same KE. Which collision is successful and explain why. Before Collision After Collision A) B) Collision B was successful due to favourable geometry. 7. Use the collision theory to explain how each factor increases the reaction rate. i) Increasing temperature ii) Increasing [reactants] iii) Increasing surface area (solid) iv) Agitation of a heterogeneous reaction v) Adding a catalyst v) i) ii) iii) more collisions and harder collisions more collisions more collisions iv) more collisions lower Ea & low energy collisions are successful 80 8. Explain why collision A was successful while collision B was unsuccessful. Before Collision After Collision A) B) Collision A was successful because it had sufficient energy. The geometry is the same for both collisions. Explain each of the following using the collision theory. You need to explain each statement. 9. a candle is not burning at room temperature a match lights the candle the candle continues to burn Exothermic H2O2 decomposes slowly at 20o C Ea is too high KI is added and rapid decomposition begins Catalyst- lowers Ea The temperature increases H2 and O2 in a balloon do not react Ea is too high A spark ignites the balloon Provides Ea Ea is too high Provides Ea 10. Exothermic 11. 81 An explosion results Exothermic CH4 and O2 in a balloon do not react Ea is too high A platinum gauze ignites the balloon Catalyst lowers Ea An explosion results Exothermic 12. 13. N2(g) + O2(g) → 2NO(g) Even though there are more than four billion collisions per second between N and O the amount of product after a year is too small to detect. Using the collision theory, give two reasons why this reaction might be slow. i) Low Temperature ii) High Ea 14. Give two reasons why some collisions will not result in a chemical reaction. i) Insufficient energy ii) Poor geometry 15. Give five reasons that might account for the following reaction having a high rate. Ca (s) + 2 HCl (aq) → CaCl2 (aq) + H2 (g) i) ii) iii) iv) v) High surface area of Ca High concentration of HCl High temperature Agitation Nature of the reactant 16. C(s) + O2(g) → CO2(g) List four ways the rate of the reaction could be increased. i) ii) iii) iv) Increase temperature Increase [ O2 ] Increase pressure Increase SA of C (add catalyst or agitate) 17. State the relationship between Activation energy and the rate of a reaction. Graph the relationship. Inverse because decreasing the activation energy increases the rate. 82 Rate Activation Energy 18. State the relationship between Temperature and the rate of a reaction. Graph the relationship. Direct, because increasing the temperature increases the rate. Rate Temperature 19. State the relationship between Concentration and the rate of a reaction. Graph the relationship. Direct, because increasing the concentration increases the rate. 83 Rate 20. Give three examples of reactions that are desired to be slow. a) b) c) 21. food spoiling corrosion of metal the fading of the colour in paint Give three examples of reactions that are desired to be fast. a) b) c) explosions the combustion of gasoline in your car when you are passing someone on the freeway the commercial production of chemicals Molarity 22. List all of the ways to increase the rate of the reaction: 2 H2O2 (aq) → 2 H2O (l) + O2 (g) Increase the H2O2 concentration Increase the Temperature Add KI catalyst 23. Describe how you would measure the rate of the reaction above. State the property you would measure and describe how it changes. Draw a diagram to illustrate your answer. 12.56 g Mass of an open container Decreases 84 or Volume of O2 See notes for diagram. Pressure of O2 in a closed system. 24. See notes for diagram. Pick the fastest and the slowest reaction at 20 °C. Slowest gases are slower than aqueous CO2(g) + 2 NaCl(aq) + H2O(l) Fastest- simple ionic or double replacement a) H2(g) + I2(g) → 2 HI(g) b) 2 HCl(aq) + Na2CO3(aq) c) Hg2+(aq) + 2 I -(aq) → → HgI2(s) 25. H2 and O2 can exist at 20 °C for years without reacting. But when a small spark ignites the mixture it reacts explosively. Explain using the Collision Theory. The activation energy is too high at room temperature so there are no successful collisions. A spark provides the kinetic energy required to overcome the Ea. Exothermic reactions produce energy. 26. Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and the x-axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy. 85 Ea (cat) Faction of collisions Ea Collision Energy 27. Shade in the area of the collision energy distribution diagram showing those collisions that do not have the required energy to be successful at the temperature below. 86 Ea Faction of collisions Collision Energy 28. Shade in the area of the collision energy distribution diagram showing those collisions that do have the required energy to be successful at the temperature below. Redraw the curve at a higher temperature. Faction of collisions Ea Higher Temperature 87 Collision Energy Kinetics - Descriptions Use the collision theory to explain the following. Each sentence must be explained with a statement from the collision theory. 1. An unlit candle does not burn. It burns after being lit with a match. It continues to burn. Ea is too high. Match is energy and provides Ea. Exothermic 2. A solution is reacting very slowly to produce bubbles. KI is added and although it is not consumed in the reaction , it speeds up the reaction rate. The temperature increases. The rate increases even more. Ea is high KI is a catalyst and lowers Ea and more collision are successful. Exothermic→ temperature increases → rate increases 3. Iron reacts slowly with HCl. Iron is replaced with Zn and a much more vigorous reaction rate occurs. Nature of reactant Fe → high Ea Zn → low Ea 4. H2 and O2 can exist together for years at room temperature without reacting. A spark begins the reaction. An explosion results. High Ea → collisions are not successful 88 A spark provides the Ea Exothermic → explosion 5. Dilute nitric acid shows little reaction with copper. Concentrated nitric acid vigorously reacts. Low concentration → few collisions High concentration → many collisions 6. Water puts out a fire. Lowers temperature so there are less collisions The collisions have less energy. 7. Paint prevents rusting. There are fewer collisions between reactant molecules. 8. A preservative in food slows rotting. The preservative is an inhibitor; which increases the Ea. Ws # 4 1. Potential Energy Diagrams Worksheet Draw the PE diagram showing the PE changes that occur during a successful collision of the exothermic reaction: H2 + I2 → 2 HI + 250 KJ The PE of the reactants = 400 KJ The activation energy of the forward reaction = 200 KJ 600 kJ/mole 400 150 Reaction path 89 2. Draw the PE diagram showing the PE changes that occur during a successful collision of the endothermic reaction: A + B + 200 KJ → C The PE of the reactants = 200 KJ The Activation Energy in the forward direction = 250 KJ 450 KJ/mole 400 200 Reaction Path 90 3. Write the following reaction in ΔH notation. A + B + 200 kJ → A + B -----> C C ΔH= +200kJ 4. Write the following reaction in Standard Notation. + I2 → H2 + I2 → H2 2 HI ΔH = -250 kJ 2HI + 250 kJ 5. Write in Standard Notation. 2NI3 + 3BaCl2 → 2NI3 2NCl3 + 3BaI2 + 3BaCl2 + 175 kJ → ΔH = 175 kJ 2NCl3 + 3BaI2 6. Write in ΔH notation. 2AlBr3 + 3BaF2 → 2AlBr3 + 3BaF2 2AlF3 + 3BaBr2 + 276 kJ → 2AlF3 + 3BaBr2 ΔH= -267 kJ Draw the potential energy diagram for the following reactions. 7. Potential energy of reactants = Potential Energy of activated complex = Potential Energy of the products = 250 kJ 350 kJ 300 kJ 91 350 KJ/mole 300 250 Reaction Path a) How does the potential energy change as the reaction proceeds? b) How does the kinetic energy change as the reaction proceeds? c) Is the reaction exothermic or endothermic? d) What is the value of ΔH? Increases Decreases Endothermic ΔH= +50kJ If a catalyst was added, what would happen to the energies of the: e) Reactants? f) Products? g) Activated Complex? h) If a catalyst was added what would happen to the rate? Draw the potential energy diagram for the following reactions. Nothing Nothing Decrease Increase 8. Potential energy of reactants = Activation Energy = Potential Energy of the products = 350 kJ 100 kJ 250 kJ 92 450 PE KJ/mol 350 250 Reaction Path a) How does the potential energy change as the reaction proceeds? b) How does the kinetic energy change as the reaction proceeds? c) Is the reaction exothermic or endothermic? d) What is the value of ΔH? Decreases Increases Exothermic ΔH= -100kJ If the concentration of the reactants was increased, what would happen to the energies of the: e) Reactants? f) Products? g) Activated Complex? h) What would happen to the rate? Draw the potential energy diagram for the following reactions. 9. Potential energy of reactants = Potential Energy of activated complex = ΔH = Nothing Nothing Nothing Increase 200 kJ 400 kJ 150 kJ 93 400 PE KJ/mol 350 200 Reaction Path a) How does the potential energy change as the reaction proceeds? b) How does the kinetic energy change as the reaction proceeds? c) Is the reaction exothermic or endothermic? d) What is the value of ΔH? If the temperature was increased, what would happen to the energies of the: e) Reactants? f) Products? g) Activated Complex? h) What would happen to the rate? 10. Potential energy of products = Potential Energy of activated complex = ΔH= Increases Decreases Endothermic ΔH= 150 kJ Nothing Nothing Nothing Increase 50 kJ 400 kJ -50 kJ 94 40 PE KJ/mol 100 50 Reaction Path a) How does the potential energy change as the reaction proceeds? b) How does the kinetic energy change as the reaction proceeds? c) Is the reaction exothermic or endothermic? d) What is the value of ΔH? Decreases Increases Exothermic ΔH= -50kJ If the surface area of the reactants was increased, what would happen to the energies of the: e) Reactants? f) Products? g) Activated Complex? h) What would happen to the rate? Nothing Nothing Nothing Increase 11. What is the only thing, other than changing the reaction that will change the potential energy diagram? Describe how it will effect the diagram and the rate. Catalyst Lowers Ea alloys more low energy collisions to be successful and increase the rate. 95 12. Label each interval on the potential energy diagram. a) a b c d e Ea (forward) (catalyzed) PE b) Ea (reverse)(catalyzed) c) ΔH d) Ea (forward) (uncatalyzed) Reaction Path e) Ea (reverse) (uncatalyzed) 12. Label each interval on the potential energy diagram. a a) b c d e Ea (forward) (uncatalyzed) PE Reaction Path b) Ea (forward) (catalyzed) 96 c) ΔH d) Ea (reverse) (uncatalyzed) e) Ea (reverse) (catalyzed) Ws # 5 Mechanisms 1. i) ii) iii) 2. i) ii) iii) iv) v) OCl- + H2O HOCl + IHOI + OHThe net chemical equation is: The reaction intermediates are: The catalyst is: Br2 → Br + OCl2 Br + Cl → → → HOCl + OHHOI + ClH2O + OI- OCl- + I- + → Cl- +OIHOCl HOI OHH2 O 2Br → → BrOCl + Cl BrCl fast slow fast The net chemical equation is: Br2 + OCl2 → BrOCl + BrCl The reaction intermediates are: Cl & Br The catalyst is: None The rate determining step is 2 If the concentration of Br2 is increased will the rate of the reaction increase? Explain your answer. No because it is not in the rate determining step. vi) If the concentration of OCl2 is increased will the rate of the reaction increase? Explain your answer. Yes because, OCl2 is in the rate determining step. 3. The mechanism for the catalytic decomposition of formic acid is shown below. 97 step 1 HCOOH + H+ step 2 [HCOOHH]+ step 3 [HCO]+ → [HCOOHH]+ → → [HCO]+ CO + HOH + H+ The potential energy diagram is: PE 190 180 170 160 150 Reaction Path i) The catalyst is H+ Crosses out from left to right ii) The rate determining step is Two Highest Ea 98 iii) ΔH = +10 kJ From start to 40 kJ Reactants to 30 kJ Products to the 160 kJ After one end iiv) The forward activation energy is the highest point iv) The reverse activation energy is highest point v) The enthalpy of [HCOOHH]+ is hump vi) Is the reaction exothermic or endothermic? Endo Uphill vii) Which chemical formula has the greatest potential energy? (HCO)+ + HOH Highest HCOOH + H+ Lowest point on graph viii) Which chemical formula has the greatest kinetic energy? point on graph ix) Does this reaction absorb or release kinetic energy? Absorb because it is endothermic (uphill) 4. Define and remember the following definitions. mechanism A sequence of steps that determines the overall reaction. activation energy The minimum energy required in a successful collision. rate determining step The slowest step in a reaction mechanism. catalyst A substance that increases the rate of a chemical reaction by providing a alternate mechanism with lower activation energy. reaction intermediate A chemical species produced in a reaction mechanism and then consumed in a later step. 99 endothermic A reaction that absorbs energy exothermic A reaction that produces energy activated complex A unstable reaction intermediate with high potential energy and low kinetic energy. ΔH The change in enthalpy or heat content for a reaction. reaction rate The change in a reactant or product per unit of time. 5. The catalyzed decomposition of acetaldehyde has an overall reaction of: CH3CHO → CH4 + CO . Determine step 2 of the reaction mechanism. A proposed mechanism is: step 1 CH3CHO step 2 HI + I2 → + CH3I CH3I + HI + CO → I2 + CH4 This is the only step 2 that will give the overall reaction below. CH3CHO → CH4 overall + CO 6. The following reaction has an overall reaction of: 2Ce4+ + Tl+ → 2Ce3+ + Tl3+ Determine step 2 of the reaction mechanism. A proposed mechanism is: step 1 Ce4+ + Mn+2 → Ce3+ + Mn3+ step 2 Ce4+ + Mn3+ → Ce3+ + Mn4+ Tl3+ + Mn2+ This is the only step 2 that will give the overall reaction below step 3 Mn4+ + Tl+ → overall 2Ce4+ + Tl+ → 2Ce3+ + Tl3+ 100 7. A reaction has a overall equation of: Br2 + OCl2 → BrOCl + BrCl . Determine step 3 of the mechanism. step 1 Br2 → 2Br step 2 Br + OCl2 → step 3 Br + Cl BrOCl + Cl → BrCl This is the only step 3 that will give the overall reaction below overall Br2 + OCl2 → BrOCl + BrCl List two intermediates: Br Cl 8. Complete the following mechanism. step 1 → NO + Pt NOPt + NO → NOPt needed for next step step 2 O2Pt + N2 O2Pt needed for next step and N2 needed to be a product step 3 O2Pt → O2 overall 2NO → N2 + Pt + O2 Identify the catalyst Pt Identify the two intermediates right to left NOPt Crosses out from left to right O2Pt Crosses out from 9. Draw a collision energy distribution diagram for a reaction where the y-axis is fraction of collisions and the x axis is collision energy. Draw the Ea line showing about 10% of the collisions having sufficient energy. Draw the Ea line for the catalyzed reaction where 20% have sufficient energy. 101 Ea cat Ea Fraction of collisions Collision Energy 10. Shade in the area of the collision energy distribution diagram showing those collisions that have the required energy to be successful at the low temperature shown below. Draw the curve that represents the distribution at a higher temperature with a different color. Shade in the area representing the successful collisions at the higher temperature with a new color. 102 Fraction of collisions Ea 103