1 CHEM 1032 FALL 2017 Practice Exam 4 1. Which f the fllwing reactins is spntaneus under nrmal and standard cnditins? A. 2 NaCl(aq) 2 Na(s) + Cl2(g) B. CaBr2(aq) + 2 H2O(aq) Ca(OH)2(aq) + 2 HBr(aq) C. AgNO3(aq) + KBr(aq) AgBr(s) + KNO3(aq) D. 3 CO2(g) + 4 H2O(g) C3H8(g) + 5 O2(g) 2. Place the fllwing gases rder f increasing mlar entrpy at STP: C3H8 CO2 N2O A. CO2 < C3H8 < N2O B. CO2 < N2O < C3H8 C. C3H8 < CO2 < N2O D. N2O < C3H8 < CO2 3. Which f the fllwing reactins has a value f ΔS that is negative? A. 2 NO(g) + O2(g) 2 NO2(g) B. NaClO3(s) Na + (aq) + ClO3 (aq) C. CH3OH(l) CO(g) + 2 H2(g) D. COCl2(g) CO(g) + Cl2(g) 4. Which f the fllwing statements is true? A. Exthermic prcesses are always spntaneus. B. Endthermic prcesses are never spntaneus. C. Endthermic prcesses increase the entrpy f the surrundings. D. Exthermic prcesses increase the entrpy f the surrundings. 5. Which f the fllwing statements is crrect? A. The ttal enthalpy f the earth is cnstant B. The entrpy f a perfect crystal at abslute zer is zer C. The ttal enthalpy f the universe is increasing D. Fr any nn-spntaneus prcess, the entrpy f the universe increases 6. The value f ΔS fr: N2H4(l) + H2(g) 2 NH3(g) is 134 J/K. Given that S fr N2H4(l) is 121 J/(ml K) and that fr H2(g) is 131 J/(ml K), what is the standard mlar entrpy f NH3(g)? A. 386 J/(ml K) B. 193 J/(ml K) C. 118 J/(ml K) D. 59 J/(ml K) 7. Estimate the value f ΔG fr: N2H4(l) + H2(g) 2 NH3(g) at 114 C, given ΔH = 142 kj and ΔS = 134 J/K. A. 157 kj B. 52,000 kj C. 194 kj D. 15,400 kj 8. Which f the fllwing relatinships is true? A. When K < 1, ΔG is negative B. ΔG = 0 at equilibrium C. When K > 1, ΔG is psitive D. ΔG = 0 at equilibrium
2 Fr questins 9-17: One f the imprtant reactins in a catalytic cnverter is: 2 CO(g) + 2 NO(g) N2(g) + 2 CO2(g). CO(g) NO(g) N2(g) CO2(g) ΔH f kj/ml 111 91.0 394 S J/(ml. K) 198 211 192 214 ΔG f kj/ml 138 88.5 394 9. Is this a redx reactin? A. Yes B. N C. Insufficient infrmatin 10. What is the xidizing agent? A. CO(g) B. NO(g) C. N2(g) D. CO2(g) 11. What is the reducing agent? A. CO(g) B. NO(g) C. N2(g) D. CO2(g) 12. The change in entrpy fr this reactin is: A. Psitive B. Negative C. Insufficient infrmatin 13. This reactin is: A. Exthermic B. Endthermic C. Insufficient infrmatin 14. At 25 C this reactin is: A. Spntaneus B. Nn-spntaneus C. Insufficient infrmatin 15. Will the reactin be spntaneus at all temperatures? A. Yes B. N C. Insufficient infrmatin 16. If the reactin was at equilibrium, i.e.: 2 CO(g) + 2 NO(g) N2(g) + 2 CO2(g), the value f the equilibrium cnstant, K, at 25 C wuld be: A. 0.76 B. 1.8 x 10 121 C. 1.3 D. 5.4 x 10 120 17. If the partial pressures f all gases was 2.0 atm, the value f ΔG at 1000 K wuld be: A. +5075 kj B. 695 kj C. 689 kj D. 683 kj
Fr questins 18-22: The redx reactin: Cr2O7 2 (aq) + NO(aq) Cr 3+ (aq) + NO3 (aq), ccurs in acidic slutin. The xidatin numbers f O and H in all reactants and prducts are 2 and +1, respectively. 18. The xidatin numbers fr Cr in Cr2O7 2 and in Cr 3+ are, respectively: A. +12 and +3 B. +6 and +3 C. +7 and +3 D. +14 and +3 19. The xidatin numbers fr N in NO and in NO3 are, respectively: A. +2 and +4 B. +1 and +3 C. +2 and +3 D. +2 and +5 20. In the reductin half reactin, each Cr atm in Cr2O7 2 : A. gains 3 e B. lses 3 e C. gains 6 e D. lses 6 e 21. In the xidatin half reactin, the N atm in NO: A. gains 3 e B. lses 3 e C. gains 6 e D. lses 6 e 22. In the balanced redx reactin: a Cr2O7 2 (aq) + b NO(g) + c H + (aq) Cr 3+ (aq) + NO3 (aq) + H2O(l) A. a = 1, b = 1, c = 10 B. a = 2, b = 1, c = 7 C. a = 1, b = 2, c = 6 D. a = 2, b = 1, c = 12 3 Fr questins 23-31: The electrchemical cell: M(s) M x+ (aq) Ag + (aq) Ag(s) was assembled and fund t prduce a vltage f +2.46 V when the cncentratin f the slutins was 1.00 M at 25 C. Use this infrmatin and the table f standard reductin ptentials: 23. The cathde is: A. M(s) B. M x+ (aq) C. Ag(s) D. Ag + (aq) 24. What is being xidized? A. M(s) B. M x+ (aq) C. Ag(s) D. Ag + (aq) 25. Electrns flw frm: A. M t Ag B. Ag t M C. Ag + t M x+ D. M x+ t Ag + 26. The catins in the salt bridge flw int the: A. ande cell B. cathde cell
4 27. If the mass f the electrdes is mnitred during the reactin we wuld find that: A. Ag decreases, M decreases B. Ag increases, M decreases C. Ag increases, M increases D. Ag decreases, M increases 28. The metal M is: A. Fe B. Al C. Mg D. Au 29. Hw many electrns are transferred frm the reducing agent t the xidizing agent? A. 1 B. 2 C. 3 D. 4 30. The value f ΔG fr the reactin at 25 C is: A. 475 kj B. +712 kj C. 237 kj D. 712 kj 31. If M x+ (aq) has a cncentratin f 2.00 M and Ag + (aq) has a cncentratin f 5.00 x 10 3 M, the cell ptential at 25 C under these nn-standard cnditins wuld be: A. +2.41 V B. +2.32 V C. +2.51 V D. +2.60 V Fr questins 32-33: Use the fllwing standard reductin ptentials: O2 + 4 H + + 4 e 2 H2O I2 + 2 e 2 I E = +1.23 V E = +0.54 V 2 H2O + 2 e H2 + 2 OH E = 0.83 V K + + e K E = 2.92 V 32. Electrlysis f mlten KI(l) will prduce: A. K(s) at the ande, I2(s) at the cathde B. I2(s) at the ande, K(s) at the cathde C. O2(g) at the ande, I2(s) at the cathde D. I2(s) at the ande, H2(g) at the cathde 33. Electrlysis f an aqueus slutin f KI(aq) will prduce: A. K(s) at the ande, I2(s) at the cathde B. I2(s) at the ande, K(s) at the cathde C. O2(g) at the ande, I2(s) at the cathde D. I2(s) at the ande, H2(g) at the cathde 34. Hw lng will it take t depsit 1.32 g f cpper frm a CuSO4(aq) slutin using a current f 0.954 amps? A. 70 min B. 60 min C. 35 min D. 4.2 x 10 3 min
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6 Useful Infrmatin: 0 ºC = 273 K R = 8.314 J/(ml K) S surr = G = H T S G = G ΔH T G = RTlnK cell cathde E = E E cell + RTlnQ ande G = nfe F = 96,485 C/ml e 1 Amp = 0.0592 E cell = lgk (at T = 25 C) n 0.0592 Ecell = E cell lgq (at T = 25 C) n 1Culmb 1secnd