Entropy Free Energy and Equilibrium Part 1

Entropy, Free Energy, and Equilibrium 1. Which of these species would you expect to have the lowest standard entropy (S°)? A) CH4(g) B) HF(g) C) NH3(g) D) H2O(g) Ans: B 2. Which of these species would you expect to have the highest standard entropy (S°)? A) CH4(g) B) C2H2(g) C) C2H4(g) D) C2H6(g) E) C3H8(g) Ans: E 3. Which of these species would you expect to have the lowest standard entropy (S°)? A) Br2(l) B) Cl2(g) C) F2(g) D) H2(g) E) I2(s) Ans: E 4. Which of these species has the highest entropy (S°) at 25°C? A) CH3OH(l) B) CO(g) C) MgCO3(s) D) H2O(l) E) Ni(s) Ans: B 5. Which of these species has the highest entropy (S°) at 25°C? A) CO(g) B) CH4(g) C) NaCl(s) D) H2O(l) E) Fe(s) Ans: B 6. Arrange these compounds in order of increasing standard molar entropy at 25°C: C3H8(g), C2H4(g), ZnS(s), and H2O(l). A) ZnS(s) < H2O(l) < C3H8(g) < C2H4(g) B) C2H4(g) < H2O(l) < C3H8(g) < NaCl(s) C) ZnS(s) < C3H8(g) < C2H4(g) < H2O(l) D) C3H8(g) < C2H4(g) < H2O(l) < ZnS(s) E) ZnS(s) < H2O(l) < C2H4(g) < C3H8(g) Ans: E 7. Arrange the following substances in the order of increasing entropy at 25°C. HF(g), NaF(s), SiF4(g), SiH4(g), Al(s) lowest highest A) SiF4(g) < SiH4(g) < NaF(s) < HF(g) < Al(s) B) HF(g) < Al(s) < NaF(s) < SiF4(g) < SiH4(g) C) Al(s) < NaF(s) < HF(g) < SiH4(g) < SiF4(g) D) Al(s) < HF(g) < NaF(s) < SiF4(g) < SiH4(g) E) NaF(s) < Al(s) < HF(g) < SiF4(g) < SiH4(g) Ans: C 8. Which one of the following reactions would you expect to have the lowest A) CH4(g) + 2O2(g) CO2(g) + 2H2O(g) B) C2H2(g) + 5/2O2(g) 2CO2(g) + H2O(g) C) C2H4(g) + O2(g) 2CO2(g) + 2H2O(g) D) C2H6(g) + 7/2O2(g) 2CO2(g) + 3H2O(g) Ans: B 9. Which one of the following reactions would you expect to have highest A) CH4(g) + 2O2(g) CO2(g) + 2H2O(g) B) C2H2(g) + 5/2O2(g) 2CO2(g) + H2O(g) C) C2H4(g) + 3O2(g) 2CO2(g) + 2H2O(g) D) C2H6(g) + 7/2O2(g) CO2(g) + 3H2O(g) Ans: D S°? S°? 10. Which response includes all the following processes that are accompanied by an increase in entropy? 1) 2SO2(g) + O2(g) SO3(g) 2) H2O(l) H2O(s) 3) Br2(l) Br2(g) 4) H2O2(l) H2O(l) + 1/2O2(g) 11. 1, 2, 3, 4 B) 1, 2 C) 2, 3, 4 D) 3, 4 E) 1, 4 Ans: D 11. Which response includes all of the following processes that are accompanied by an increase in entropy? 1) I2(s) I2(g) 2) 2I(g) I2(g) 3) 2NH3(g) N2(g) + 3H2(g) 4) Mg2+(aq) + 2OH–(aq) Mg(OH)2(s) 12. 1, 2 B) 1, 3 C) 3, 4 D) 3 E) 2, 4 Ans: B 12. Which response includes all of the following processes that are accompanied by an increase of entropy? A) I and III Ans: A B) II and III C) I, II and III D) II only E) III only 13. Without reference to a table, arrange these reactions according to increasing S. 1) CH4(g) + H2O(g) CO(g) + 3H2(g) 2) C(s) + O2(g) CO2(g) 3) H2O2(l) H2O(l) + 1/2O2(g) 14. 1 < 3 < 2 B) 2 < 3 < 1 C) 2 < 1 < 3 D) 3 < 2 < 1 E) 3 < 1 < 2 Ans: B 14. Arrange these reactions according to increasing S. 1) H2O(g) H2O(l) 2) 2NO(g) N2(g) + O2(g) 3) MgCO3(s) MgO(s) + CO2(g) 15. 1 < 2 < 3 B) 2 < 3 < 1 C) 3 < 2 < 1 D) 2 < 1 < 3 E) 1 < 3 < 2 Ans: A 15. Which of the following processes would be accompanied by an increase in entropy? A) H2O(g) H2O(s) D) H2O(s) H2O(g) B) H2O(l) H2O(s) E) H2O(l, 50°C) H2O(l, 25°C) C) H2O(g) H2O(l) Ans: D 16. Which of the following processes would be accompanied by a decrease in entropy? A) H2O(s) H2O(g) D) H2O(g) H2O(s) B) H2O(l) H2O(g) E) H2O(l, 50°C) H2O(l, 75°C) C) H2O(s) H2O(l) Ans: D 17. Which of the following is expected to have zero entropy? I. N2(g) at 273 K II. SiO2(s, amorphous) at 0 K III. NaCl(s) perfectly ordered crystal at 25 K IV. Na(s) perfectly ordered crystal at 0 K A) I and IV B) III and IV C) I and II D) I, II, and III E) IV only Ans: E 18. Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk  Al(s) O2(g) Al2O3(s) S°(J/K·mol) 28.3 205.0 50.99 A) B) C) Ans: D) E) 182.3 J/K·mol 131.5 J/K·mol –182.3 J/K·mol D –626.2 J/K·mol –802.9 J/K·mol 19. Sulfur can be separated from lead in the mineral galena, PbS(s), by “roasting” the ore in  PbS(s) O2(g) PbO(s) SO2(g) A) B) C) Ans: –410 J/K·mol –161.5 J/K·mol –47.7 J/K·mol B 20. Determine A) B) C) Ans: A) B) C) Ans: D) E) S° for the reaction SO3(g) + H2O(l) S°(J/K·mol) SO3 256.2 H2O 69.9 H2SO4 156.9 169.2 J/K·mol 1343.2 J/K·mol –169.2 J/K·mol C 21. Calculate S°(J/K·mol) 91.2 205.0 69.45 248.5 21.8 J/K·mol 43.5 J/K·mol H2SO4(l). D) E) –29.4 J/K·mol 29.4 J/K·mol S° for the reaction SO2(s) + NO2(g) S°(J/K·mol) SO2(g) 248.5 SO3(g) 256.2 NO(g) 210.6 NO2(g) 240.5 SO3(g) + NO(g). D) E) 474.8 J/K·mol –474.8 J/K·mol 53.6 J/K·mol –53.6 J/K·mol –22.2 J/K·mol C 22. Calculate S° at 25°C for the reduction of PbO(s), 2PbO(s) + C(s) given these absolute entropies: S° (J/K·mol) PbO(s) 69.45 C(s) 5.7 Pb(s) 64.89 CO2(g) 213.6 A) B) C) Ans: +198.8 J/K·mol +488.0 J/K·mol +353.6 J/K·mol A D) E) 2Pb(s) + CO 2(g) –203.3 J/K·mol +203.3 J/K·mol 23. Which of the following is consistent with a spontaneous process in the forward direction? A) Suniv > 0, G < 0, T Suniv > 0 D) Suniv < 0, G < 0, T Suniv < 0 B) Suniv < 0, G > 0, T Suniv < 0 E) Suniv > 0, G > 0, T Suniv > 0 C) Suniv > 0, G < 0, T Suniv < 0 Ans: A 24. Which of the following is consistent with a nonspontaneous process in the forward direction? A) Suniv > 0, G < 0, T Suniv > 0 D) Suniv < 0, G < 0, T Suniv < 0 B) Suniv < 0, G > 0, T Suniv < 0 E) Suniv > 0, G > 0, T Suniv > 0 C) Suniv > 0, G < 0, T Suniv < 0 Ans: B 25. HI has a normal boiling point of –35.4°C, and its Hvap is 21.16 kJ/mol. Calculate the molar entropy of vaporization ( Svap). D) 0.068 J/K·mol A) 598 J/K·mol E) 89.0 J/K·mol B) 68.6 J/K·mol C) 75.2 J/K·mol Ans: E 26. With respect to the system only, a reaction with be: A) Spontaneous at all temperatures B) Spontaneous at high temperatures only C) Spontaneous at low temperatures only D) Nonspontaneous at all temperatures Ans: D H > 0 and S < 0 is predicted to 27. With respect to the system only, a reaction with H < 0 and S > 0 is predicted to be: A) Spontaneous at all temperatures B) Spontaneous at high temperatures only C) Spontaneous at low temperatures only D) Nonspontaneous at all temperatures Ans: A 28. Which of the following is consistent with a spontaneous endothermic reaction? A) H > 0, S < 0, G < 0  B) H > 0, S > 0, G < 0 C) H < 0, S < 0, G < 0 Ans: B 29. Which of the following is consistent with an exothermic reaction that is spontaneous at all temperatures? A) H > 0, S < 0, G < 0  B) H > 0, S > 0, G < 0 C) H < 0, S < 0, G < 0 Ans: D 30. Which of the following is consistent with an exothermic reaction that is nonspontaneous at high temperatures? A) H > 0, S < 0, G < 0  B) H > 0, S > 0, G < 0 C) H < 0, S > 0, G < 0 Ans: E 31. Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk metal from further corrosion. 4Al(s) + 3O2(g) 2Al2O3(s) Calculate G° for this reaction, given that G°f of aluminum oxide is –1576.4 kJ/mol. A) –3152.8 kJ/mol D) 1576.4 kJ/mol B) –1576.4 kJ/mol E) 3152.8 kJ/mol C) –788.2 kJ/mol Ans: A 32. Calculate G° for the reaction 3NO2(g) + H2O(l) H2O(l) HNO3(l) NO(g) NO2(g)  G°f (kJ/mol) –237.2 –79.9 86.7 51.8 2HNO3(l) + NO(g). A) B) C) Ans: 8.7 kJ/mol 192 kJ/mol –414 kJ/mol A D) E) –192 kJ/mol –155 kJ/mol 33. Ozone (O3) in the atmosphere can reaction with nitric oxide (NO):  A) B) C) Ans: 1020 kJ/mol –1.22 × 103 kJ/mol 2.00 × 103 kJ/mol E D) E) –1.42 × 103 kJ/mol –198 kJ/mol 34. Sodium carbonate can be made by heating sodium bicarbonate: 2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g) Given that H° = 128.9 kJ/mol and G° = 33.1 kJ/mol at 25°C, above what minimum temperature will the reaction become spontaneous under standard state conditions? A) 0.4 K B) 3.9 K C) 321 K D) 401 K E) 525 K Ans: D 35. The element oxygen was prepared by Joseph Priestley in 1774 by heating mercury(II) oxide: HgO(s) Hg(l) + 1/2O2(g), H° = 90.84 kJ/mol. Estimate the temperature at which this reaction will become spontaneous under standard state conditions. S°(Hg) = 76.02 J/K·mol S°(O2) = 205.0 J/K·mol S°(HgO) = 70.29 J/K·mol A) 108 K B) 430 K C) 620 K D) 775 K E) 840 K Ans: E 36. For the reaction H2(g) + S(s) H2S(g), H° = –20.2 kJ/mol and S° = +43.1 J/K·mol. Which of these statements is true? A) The reaction is only spontaneous at low temperatures. B) The reaction is spontaneous at all temperatures. C) G° becomes less favorable as temperature increases. D) The reaction is spontaneous only at high temperatures. E) The reaction is at equilibrium at 25°C under standard conditions. Ans: B 37. The normal freezing point of ammonia is –78°C. Predict the signs of H, S, and G for ammonia when it freezes at –80°C and 1 atm: NH3(l) NH3(s) A) A B) B Ans: E C) C D) D E) E 38. The normal melting point sulfur is 113 °C. If a sample of solid sulfur is at 95 °C, Predict  A) H > 0, S > 0, G < 0  B) H > 0, S > 0, G > 0 C) H > 0, S < 0, G < 0 Ans: B 39. The normal boiling point of acetic acid is 118.1°C. If a sample of the acetic acid is at  A) H > 0, S > 0, G < 0  B) H > 0, S > 0, G > 0 C) H > 0, S < 0, G < 0 Ans: A  A) B) C) Ans: 105 kJ/mol 1.07 kJ/mol –233 kJ/mol E Category: Medium D) E) –105 kJ/mol 233 kJ/mol Section: 17.6 42. Calculate Kp at 298 K for the reaction SO2(g) + NO2(g) SO2(g) SO3(g) NO(g) NO2(g)  G°f –300.4 kJ/mol –370.4 kJ/mol 86.7 kJ/mol 51.8 kJ/mol SO3(g) + NO(g). A) 6.99 × 10–7 Ans: E B) 5.71 × 10–8 C) 14.2 D) 475 E) 1.42 × 106 43. The equilibrium constant at 427°C for the reaction N2(g) + 3H2(g) 2NH3(g) is Kp = 9.4 × 10–5. Calculate the value of G° for the reaction under these conditions. A) –33 kJ/mol B) –54 kJ/mol C) 54 kJ/mol D) 33 kJ/mol E) 1.3 J/mol Ans: C 44. Determine the equilibrium constant Kp at 25°C for the reaction N2(g) + 3H2(g) 2NH3(g) [G°f (NH3(g)) = –16.6 kJ/mol]. A) 1.52 × 10–6 B) 6.60 × 105 C) 8.28 × 10–2 D) 2.60 E) 13.4 Ans: B  B) G = –69.1 kJ/mol, spontaneous C) G = 97.5 kJ/mol, spontaneous Ans: D E) G = –97.5 kJ/mol, nonspontaneous 48. For the reaction 2C(graphite) + H2(g) C2H2(g), G°= +209.2 kJ/mol at 25°C. If P(H2) = 100. atm, and P(C2H2) = 0.10 atm, calculate G for this reaction. A) +207.8 kJ/mol D) +17.3 kJ/mol B) +226.3 kJ/mol E) –16.9 kJ/mol C) +192.1 kJ/mol Ans: C 49. For the reaction 2 SO2(g) + O2(g) 2 SO3(g), if initially P(SO2) = 1.2 atm, P(O2) = 1.8 atm, and P(SO3) = 2.1 atm, calculate G for this reaction at 25°C. The following data is valid at 25°C: SO2 SO3 A) B) C) Ans: Gf° (kJ/mol) –300.4 –370.4 D) E) –140.0 kJ/mol –137.6 kJ/mol –138.7 kJ/mol C 1,174.7 kJ/mol –141.3 kJ/mol 50. For the reaction 2NO(g) + O2(g) 2NO2(g) if initially P(NO) = 1.5 atm, P(O2) = 1.4 atm, and P(NO2) = 2.0 atm, calculate G for this reaction at 25°C. The following data is valid at 25°C: NO NO2 A) B) C) Ans: Gf° (kJ/mol) 86.7 51.8 D) E) –69.9 kJ/mol –69.2 kJ/mol 522.1 kJ/mol B –79.9 kJ/mol –35.0 kJ/mol 51. Determine the equilibrium constant (Kp) at 25°C for the reaction G° = –28.5 kJ/mol. CO(g) + H2O(g) CO2(g) + H2(g) A) 2.9 × 10–60 Ans: D B) 1.0 × 10–4 C) 1.2 D) 1.0 × 105 E) 3.4 × 1059 52. Kw for the auto-ionization of water, H2O(l) H+(aq) + OH– (aq), is 1.0 × 10–14. What are    Ans: A 53. Which of the following is consistent with a reaction at equilibrium? D) G < 0, Q = K A) G = 0, Q = K B) G° = 0, Q > K E) G° = 0, Q < K C) G > 0, Q = K Ans: A 54. Which of the following is consistent with a reaction that proceeds spontaneously in the forward direction? A) G > 0, Q < K  B) G° = 0, Q = K C) G < 0, Q > K Ans: E 55. Which of the following is consistent with a reaction that proceeds spontaneously in the reverse direction (assume all variables are in terms of the forward direction only)? A) G > 0, Q < K  B) G° = 0, Q = K C) G < 0, Q > K Ans: E 56. The reaction rates of many spontaneous reactions are actually very slow. Which of these statements is the best explanation for this observation? A) Kp for the reaction is less than one. B) The activation energy of the reaction is large. C) G° for the reaction is positive. D) Such reactions are endothermic. E) The entropy change is negative. Ans: B 57. The solubility product constant at 25°C for AgI(s) in water has the value 8.3 × 10–17. Calculate Grxn at 25°C for the process AgI(s) Ag+(aq) + I– (aq) where [Ag+] = 9.1 × 10–9 and [I–] = 9.1 × 10–9. A) +4.4 kJ/mol D) –91.7 kJ/mol E) –4.4 kJ/mol B) +91.7 kJ/mol C) 0.0 kJ/mol Ans: C 58. Calculate G° for the combustion of ethanol vapor, C2H5OH(g), at 750°C in oxygen to form carbon dioxide and water vapor. The following data is valid at 25°C: C2H5OH(g) O2(g) H2O(g) CO2(g) A) B) C) Ans: –1407 kJ/mol –2151 kJ/mol –1307 kJ/mol E  H°f (kJ/mol) –234.8 0 –241.8 –393.5  G°f (kJ/mol) –167.9 0 –228.6 –394.4 D) E) –4486 kJ/mol –1377 kJ/mol