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CHEMISTRY 102B/C Hour Exam III Fall 2014 Page 1 1. Consider the following reaction: 4 NO2(g) + O2(g) ⇌ 2 N2O5(g) K = 6.2 × 106 If 4.0 moles of NO2 and 4.0 mol of O2 are placed in a 2.0 L container, what is the equilibrium concentration of N2O5? a) 1.4 × 102 M b) 4.0 × 102 M d) 7.0 × 103 M e) 2.5 × 103 M c) 8.0 × 102 M Consider the following data for the next two questions: Specific heat capacity of ice = 2.03 J/C g Specific heat capacity of water = 4.18 J/C g Specific heat capacity of steam = 2.02 J/C g Hfusion = 6.02 kJ/mol Hvaporization = 40.7 kJ/mol 2. Consider a 1.00 mole sample of ice at 30.0C, which is heated to steam at 140.0C. Calculate q for the entire process. a) 123 kJ 3. b) 1070 kJ d) 234 kJ e) 56.8 kJ A 500.0 g sample of an element at 195C is dropped into an ice-water mixture. 109.5 g of ice melts and an ice-water mixture remains. Calculate the specific heat capacity of the element. a) 2.67 J/C g 4. c) 6.75 kJ b) 0.375 J/C g c) 0.789 J/C g Which of the following mathematical relationships is false? a) Esystem = Esurroundings b) At constant pressure, q = E + PV. c) Hsystem Huniverse = Hsurroundings d) At constant volume, E = q. e) For a cyclic process, w = q. d) 1.62 J/C g CHEMISTRY 102B/C Hour Exam III 5. Fall 2014 Page 2 Consider the following reaction: 2 NO2(g) ⇌ 2 NO(g) + O2(g) K=? 4.0 moles of NO2 are placed in a 1.0 L container and are allowed to react to reach equilibrium. At equilibrium the concentration of NO(g) is 1.0 M. Calculate the value of the equilibrium constant, K, for this reaction. a) 0.056 6. c) 0.17 d) 25 e) 590 The Ksp value for BaF2 is 5.0 × 107. When 10.0 mL of 0.010 M NaF is mixed with 10.0 mL of 0.010 M Ba(NO3)2, will a precipitate form? a) b) c) d) 7. b) 0.11 No, because Q = 1.0 × 106 and since it is greater than Ksp, no precipitate will form. Yes, because Q = 1.0 × 106 and since it is greater than Ksp, a precipitate will form. No, because Q = 1.3 × 107 and since it is less than Ksp, no precipitate will form. Yes, because Q = 1.3 × 107 and since it is less than Ksp, a precipitate will form. The reaction for the formation of the complex ion Cu(NH3)42+ is: Cu2+(aq) + 4 NH3(aq) Cu(NH3)42+(aq) Which of the following is the correct expression for the equilibrium constant, K, for this reaction? 2 2 8. a) K [Cu(NH3 )4 ] [Cu 2 ][NH3 ] b) K [Cu(NH3 )4 ]4 [Cu 2 ][NH 3 ]4 d) K 1 2 [Cu ][NH3 ]4 e) K [Cu(NH3 )4 ] [Cu 2 ][NH 3 ]4 c) K 1 [Cu ][NH3 ] 2 2 The heat capacity of a bomb calorimeter was determined by combusting 6.79 g of CH4 (energy of combustion of CH4 = 802 kJ/mol CH4); the temperature of the bomb calorimeter increased by 10.8C. In a second experiment with the same bomb calorimeter, combustion of a 12.6 g sample of ethyne, C2H2, produced a temperature increase of 16.9C. Calculate the energy of combustion of C2H2 in kJ/mol. a) 31.4 kJ/mol b) 1.10 × 103 kJ/mol d) 532 kJ/mol e) 340. kJ/mol c) 1.47 × 103 kJ/mol CHEMISTRY 102B/C Hour Exam III 9. Fall 2014 Page 3 Consider the following reaction which has an enthalpy change of HT: AX H = HT This reaction can be broken down into a series of steps as shown in the following diagram: Which of the following relationships must be true for this reaction? a) HT H1 H2 H3 = 0 b) H2 (H3 + H1) = HT c) HT + H1 + H2 + H3 = 0 d) HT + H2 = H1 + H3 e) H3 (H1+ H2) = 0 10. Consider the following reaction at some temperature: Cl2(g) + F2(g) ⇌ 2 ClF(g) Kp = 16 If initially 3.00 atm of F2 and 3.00 atm of Cl2 are reacted in a rigid container, calculate the equilibrium partial pressure of Cl2(g). 11. a) 0.25 atm b) 0.50 atm d) 1.5 atm e) 2.0 atm c) 1.0 atm A 50.0 mL sample of 0.200 M Ca(NO3)2 is mixed with 50.00 mL of 0.200 M NaF. When the system has come to equilibrium, what are the equilibrium concentrations of Ca2+ and F? Ksp for CaF2 = 4.0 × 1011. a) b) c) d) e) [Ca2+]e 5.0 × 102 M 1.0 × 101 M 2.2 × 104 M 1.0 × 101 M 5.0 × 102 M [F]e 1.4 × 105 M 1.0 × 105 M 4.3 × 104 M 2.0 × 105 M 2.8 × 105 M CHEMISTRY 102B/C Hour Exam III 12. Fall 2014 Page 4 Silver acetate (AgC2H3O2) is a sparingly soluble salt with Ksp = 1.9 × 103. Compare the effects on the solubility of silver acetate by addition of HNO3 or by addition of NH3. a) Addition of either HNO3 or NH3 would decrease the solubility of AgC2H3O2. b) Addition of NH3 would increase the solubility of AgC2H3O2, but addition of HNO3 would decrease it. c) Addition of NH3 would increase the solubility of AgC2H3O2, but addition of HNO3 would have virtually no effect. d) Addition of either HNO3 or NH3 would increase the solubility of AgC2H3O2. e) Addition of NH3 would decrease the solubility of AgC2H3O2, but addition of HNO3 would increase it. 13. Using the bond energies below, estimate the enthalpy change in kJ for the reaction: Bond Energy (kJ/mol) CH 413 CO 358 C=O 745 OH 467 CC 347 HH 432 14. a) H = 2654 kJ b) H = 567 kJ d) H = 0 kJ e) H = 1258 kJ c) H = 567 An equilibrium mixture for the reaction: 2 NH3(g) ⇌ N2(g) + 3 H2(g) K=? contains 9.0 mol N2, 6.0 mol H2, and 6.0 mol NH3, all in a 3.0 L container at a certain temperature. Calculate the value of K for this reaction at this temperature. a) 2.0 b) 4.0 d) 9.0 e) 12 c) 6.0 CHEMISTRY 102B/C Hour Exam III 15. 16. 17. Fall 2014 Page 5 Aluminum fluoride has a solubility of 6.66 × 102 mol/L. Calculate the Ksp value for AlF3(s). a) 4.44 × 103 b) 1.97 × 105 d) 5.31 × 104 e) 5.90 × 106 c) 5.90 × 105 Calculate the molar solubility of Ag2CO3(s) in an aqueous solution that is 0.50 M in K2CO3. Ksp for Ag2CO3 = 8.2 × 1012 a) 2.0 × 106 mol/L b) 2.6 × 104 mol/L d) 2.8 × 106 mol/L e) 3.4 × 103 mol/L c) 1.3 × 104 mol/L Given the following set of gas phase reactions: H2 + Cl2 2 HCl H2 2 H Cl2 2 Cl H = 184 kJ H = 432 kJ H = 240 kJ calculate the bond energy of the HCl bond. a) 248 kJ 18. b) 428 kJ c) 864 kJ d) 92 kJ e) 184 kJ Determine E for a system which undergoes both of the following two processes: I. 15 J of work is done on the system, while 30 J of heat is absorbed by it; then: II. 20 J of heat is given off by the system, while 25 J of work is done by the system. a) 30 J 19. b) 30 J c) 40 J d) 45 J e) 0 Consider the reaction: NH4NO3(s) ⇌ N2O(g) + 2 H2O(g) K = 4.85 200. g of NH4NO3(s) are placed in a reaction vessel containing H2O(g) at a concentration of 2.0 M and N2O(g) at a concentration of 2.0 M. After equilibrium is reached, will the mass of NH4NO3(s) increase, decrease or remain unchanged? a) The mass of NH4NO3(s) will decrease (< 200. g). b) The mass of NH4NO3(s) will increase (> 200. g). c) The mass of NH4NO3(s) will remain unchanged (= 200. g). CHEMISTRY 102B/C Hour Exam III 20. Fall 2014 Page 6 Consider the following endothermic reaction at equilibrium: SiHCl3(g) + 3 H2O(g) ⇌ SiH(OH)3(s) + 3 HCl(g) Which of the following would cause the reaction to shift toward reactants (shift left) to reestablish equilibrium? a) b) c) d) e) 21. Adding H2O(g). Increasing the temperature. Adding Ar(g) (assume a constant volume container). Increasing the volume of the reaction container. Adding SiH(OH)3(s). How many of the following five quantities is/are state functions? I. work IV. pressure a) none 22 II. enthalpy V. temperature b) 1 c) 2 III. highway distance from Peoria to Champaign d) 3 e) 5 (All are state functions.) Consider the reaction: Ca3P2(s) + 6 H2O(l) 3 Ca(OH)2(s) + 2 PH3(g) H = 721.70 kJ If this reaction were carried out at 298 K in a beaker open to a constant-pressure atmosphere, which of the following would be false? 23. a) E = 716.74 kJ b) w = 4.96 kJ d) The reaction is exothermic. e) Heat is released. c) qp = 721.70 kJ The following reaction was studied in a coffee cup calorimeter: 2 HCl(aq) + Ba(OH)2(aq) BaCl2(aq) + 2 H2O(l) H = 118 kJ In the coffee cup calorimeter, 100.00 mL of 0.500 M HCl was mixed with 300.0 mL of 0.500 M Ba(OH)2. Assuming a solution density of 1.00 g/mL, a solution heat capacity of 4.18 J/C g, an initial solution temperature of 25.00C, and no heat loss to the coffee cups, calculate the final temperature of the reaction mixture. a) 23.24C b) 25.92C c) 2.89C d) 27.89C e) 26.76C CHEMISTRY 102B/C Hour Exam III 24. When ethene gas, C2H4, is combusted at 298 K, CO2(g) and H2O(l) are produced. The enthalpy of combustion of ethene at 298 K is 1411.1 kJ/mol ethene. Given the following standard enthalpies of formation, calculate the standard enthalpy of formation for ethene. Hf 393.5 kJ/mol 285.9 kJ/mol CO2(g) H2O(l) 25. 26. Fall 2014 Page 7 a) 52.3 kJ/mol b) 731.7 kJ/mol d) 126.2 kJ/mol e) 296.0 kJ/mol c) 2769.9 kJ/mol The solubility of La(IO3)3 in a 0.10 M KIO3 solution is 1.0 × 107 mol/L. Calculate the Ksp value for La(IO3)3. a) 1.0 × 108 b) 2.7 × 109 d) 2.7 × 1027 e) 6.2 × 108 c) 1.0 × 1010 Consider the following five reactions: I. P4(s) + 6 Cl2(g) 4 PCl3(g) II. P4(s) + 5 O2(g) P4O10(g) III. PCl3(g) + ½ O2(g) Cl3PO(l) IV. PCl3(g) + Cl2(g) PCl5(g) V. P4O10(s) + 6 PCl5(g) 10 Cl3PO(l) For which reaction should bond energies give the best estimation for Hreaction? a) I 27. b) II c) III d) IV e) V Which of the following compounds has the smallest molar solubility (mol/L) in water? a) Al(OH)3 Ksp = 2 × 1032 b) CdS Ksp = 1 × 1028 c) PbSO4 Ksp = 1 × 108 d) Sn(OH)2 Ksp = 3 × 1027 e) MgC2O4 Ksp = 9 × 105 CHEMISTRY 102B/C Hour Exam III 28. Fall 2014 Page 8 Consider two salts, PbX2 and PbY2, both of which have very similar Ksp values. Assuming HX is a strong acid and HY is a weak acid, which salt is more soluble in acidic solution? a) PbX2 b) PbY2 c) They should be equally soluble in acidic solution. 29. The standard enthalpy of formation for liquid water is 286 kJ/mol. For which of the following reactions does Hreaction = 286 kJ? a) H2O(l) 2 H(g) + O(g) b) 2 H(g) + O(g) H2O(l) c) H2(g) + ½ O2(g) H2O(l) d) H2O(l) H2(g) + ½ O2(g) e) H2O(g) H2O(l) 30. Consider when 1.0 mole of A(g) and 1.0 mole of B(g) are added to a 2.0 L container and the following balanced reaction occurs: A(g) + 2 B(g) ⇌ 2 C(g) + 3 D(g) Which of the following statements must be true regarding this reaction once equilibrium has been reached? a) The value of the equilibrium constant for this reaction must be greater than 1 (K > 1). b) The value of the equilibrium constant for this reaction must be greater than 1 (K < 1). c) At equilibrium, the rate of the reverse reaction must be greater than the rate of the forward reaction. d) At equilibrium, the concentration of B(g) must be equal to the concentration of C(g) ([B]e = [C]e). e) At equilibrium, the concentration of B(g) must be smaller than the concentration of A(g) ([B]e < [A]e). 31. My chemistry 102 exam should be graded with the answer sheet associated with: a) Form A b) Form B c) Form C d) Form D e) Form E