Chapter 18

14. If a chemical reaction occurs in a direction that has a positive change in entropy, then _____.

the disorder of the system increases.

19. Arrange the following reactions in order of increasing ΔrS° value: 1.H2(g) + F2(g) → 2HF(g) 2.NH4NO3(s) → N2O(g) + 2H2O(l) 3.(NH4)2Cr2O7(s) → Cr2O3(s) + 4H2O(l) + N2(g)

1 < 2 < 3

50. Calculate ΔrG° for the reaction below at 25.0 °C. CH4(g) + H2O(g) → 3 H2(g) + CO(g) Given: ΔfG° [CH4(g)] = -50.8 kJ/mol, ΔfG° [H2O(g)] = -228.6 kJ/mol, ΔfG° [H2(g)] = 0.0 kJ/mol, and ΔfG° [CO(g)] = -137.2 kJ/mol.

+142.2 kJ/mol-rxn

26. The standard entropy for the formation of sulfur hexafluoride from the sulfur and fluorine is -348.7 J/K ⋅mol-rxn at 298.15 K. What is the standard molar entropy of sulfur hexafluoride for the reaction below? (Given: S°[S(s)] = 32.1 J/K ⋅mol and S°[F2(g)] = 202.8 J/K ⋅mol)

+291.8 J/K⋅mol

28. Use the given thermodynamic data and the reaction below to calculate ΔS°(universe) for the formation of Fe2O3(s) at 298.15 K.3 Fe(s) + 2 O2(g) → Fe3O4(s) Species ΔfH° (kJ/mol) S° (J/K⋅mol) Fe(s) 0.0 27.8 O2(g) 0.0 205.1 Fe3O4(s) -1118.4 146.4

+3404 J/K

27. Calculate ΔS°(universe) for the combustion of acetylene at 298.15 K using the reaction below. (Given: ΔS°(system) = -194.6 J/K and ΔH°(system) = -2511.2 kJ) 2 C2H2(g) + 5 O2(g) → 4 CO2(g) + 2 H2O(g)

+8228.0 J/K

48. Calculate ΔG° at 298 K for the reaction below. I2(g) + Br2(g) → 2IBr(g) Given: ΔrH° = -11.6 kJ/mol-rxn; ΔrS° = 12 J/K⋅mol-rxn at 298 K.

-15.2 kJ/mol-rxn

24. Calculate the standard entropy change for the following reaction: 2 SO2(g) + O2(g) → 2 SO3(g) Given: S°[SO2(g)] = 248.2 J/K⋅mol, S°[O2(g)] = 205.1 J/K⋅mol, and S°[SO3(g)] = 256.8 J/K⋅mol.

-187.9 J/K·mol-rxn

51. Determine ΔfG° at 298 K for SnO using the data below. Sn(s) + SnO2(s) → 2SnO(s) Given: ΔrG° = 12.0 kJ/mol-rxn at 298K. Substance ΔfG°(kJ/mol) at 298 K SnO(s) ? SnO2(s) -515.8

-251.9 kJ/mol

49. Calculate ΔrG° at 25.0 °C for the reaction below. 2 Na(s) + 2 H2O() → 2 NaOH(aq) + H2(g) Given: ΔrH° = −366.6 kJ/mol-rxn and ΔrS° = −154.2 J/K⋅mol-rxn.

-320.6 kJ/mol-rxn

53. Using the given data, determine ΔrG° at 500.0 K for the reaction below. Ba(s) + H2O(g) → BaO(s) + H2(g) Substance ΔfH°(kJ/mol-rxn) at 298 KS° (J/K·mol-rxn) at 298 K Ba(s) 0 62.8 H2O(g) -241.8 188.7 BaO(s) -592 70.4 H2(g) 0 130.6

-325.0 kJ/mol-rxn

52. Using the given data, determine ΔrG° at 298 K for the precipitation reaction below. Ag+(aq) +Br−(aq) → AgBr(s) Substance ΔfG°(kJ/mol) at 298 K Br−(aq) -104.0 Ag+(aq) 77.12 AgBr(s) -96.9

-70.0 kJ/mol-rxn

55. Given the following data: S(g) + O2(g) → SO2(g) ΔrG° = -300.1 kJ/mol-rxn 2 S(g) + 3 O2(g) → 2 SO3(g) ΔrG° = -742.1 kJ/mol-rxn Calculate ΔfG° for the reaction below.SO2(g) + 1/2 O2(g) → SO3(g)

-71.0 kJ/mol-rxn

23. What is the standard entropy change for the following reaction? 4 N2(g)+ 12 H2(g)→8 NH3(g) (J/mol⋅K) 191.5 130.6 192.3

-794.8 J/K⋅mol-rxn

1. When a chemical process occurs under standard conditions, which of the following conditions always apply? 1.Gaseous species are at a pressure of 1 bar. 2.The solution concentration is 1 molal. 3.The temperature is 298.15 K.

1 and 2

4. The following processes occur spontaneously at 25 °C. Which of these processes is/are endothermic? 1.Ammonium nitrate, NH4NO3, dissolving in water (which is accompanied by a cooling of the water). 2.The expansion of a real gas into a vacuum (which is accompanied by a cooling of the gas). 3.Liquid water in an ice cube tray freezing into ice after being placed in a freezer.

1 and 2

5. Which of the following statements is/are correct? 1.Spontaneous changes only occur in the direction that leads to equilibrium. 2.Exothermic reactions are always spontaneous. 3.In any chemical reaction, energy must be conserved.

1 and 3

61. The standard free energy change for a chemical reaction is +13.3 kJ/mol. Which of the following is the equilibrium constant for the reaction at 125 °C? (R = 8.314 J/K⋅mol)

1.8 × 10^-2

68. The standard free energy of formation of AgI(s) is -66.2 kJ/mol. ΔrG° for the reaction 2AgI(s) → 2Ag(s) + I2(s) is:

132.4 kJ

62. The standard free energy change associated with the dissolution of ammonium nitrate in water is -6.73 kJ/mol at 298.15 K. NH4NO3(s) ----> NH4NO3(aq) Which of the following is the equilibrium constant for the reaction? (R = 8.314 J/K⋅mol)

15

17. For which of the following reactions will the entropy of a system decrease?

2 NO2(g) → N2O4(g)

3. Which of the following statements concerning entropy change is/are true? 1.For a reversible process, . 2.For a spontaneous process, . 3.For a reversible process, such as a phase change, ΔS = qrev/T .

2 and 3

15. Which of the following reactions would be expected to have a positive entropy change, ΔrS° > 0? 1. 2 SO2(g) + O2(g) → 2 SO3(g) 2. Ba(OH)2(s) → BaO(s) + H2O(g) 3. CO(g) + 2 H2(g) → CH3OH(l)

2 only

66. Calculate ΔrG° for the reaction below at 425 °C, 2 HI(g) H2(g) + I2(g); K = 0.018. (R = 8.314 J/K⋅mol)

2.33 × 10^4 kJ/mol-rxn

9. Which of the following represents the change in entropy for a system going from 142 possible microstates to 830 possible microstates? (k = 1.381 × 10-23 J/K)

2.44 x 10^-23 J/K

64. What is the equilibrium constant for reaction below at 25 °C? (R = 8.314 J/K⋅mol) 2 NO(g) + O2(g) 2 NO2(g); ΔfG° [NO(g)] = +86.6 kJ/mol and ΔfG° [NO2(g)] = +51.2 kJ/mol.

2.6 × 10^12

31. A change of state occurring in a system is accompanied by 60.7 kJ of heat that is transferred to the surroundings at a constant pressure and at a constant temperature of 300 K. Calculate the ΔS(surroundings) for the process.

202 J/K

25. What is the S0 for ozone if the standard entropy change for the reaction below is 411 J/K⋅mol-rxn and S0[O2(g)] = 205 J/K⋅mol. 6 O3(g) → 9 O2(g)

239 J/K⋅mol-rxn

6. For a certain reversible process, q = 88.06 kJ at 29.4°C. Which of the following is the ΔS for the process?

291 J/K

12. Which of the following statements concerning entropy is/are correct? 1.The entropy of a substance increases when converted from a liquid to a solid. 2.The entropy of a substance decreases as its temperature increases. 3.All substances have positive entropy values at temperatures above 0 K.

3 only

63. Which of the following is the equilibrium constant for the reaction below at 25 °C? (R = 8.314 J/K ⋅mol)MgCO3(s) MgO(s) + CO2(g); ΔfG° [MgCO3(s)] = -1028.2 kJ/mol, ΔfG [MgO(s)] = -568.8 kJ/mol, and ΔfG° [CO2(g)] = -394.4 kJ/mol.

4.0 × 10^-12

67. What is the equilibrium constant for the reaction below at 298 K? 2C(s) + 3H2(g) → C2H6(g) Given: ΔrH° = -84.68 kJ; ΔrS° = -173.8 J/K at 298 K. (R = 8.314 J/K⋅mol)

5.8 × 10^5

47. For a reaction, ΔrH° = -208.8 kJ and ΔrS° = -308.2 J/K. At what temperature will ΔrG° = 0.00 kJ?

677.5 K

56. Estimate the boiling point of ethanol, C2H5OH, using the given the following thermodynamic parameters. C2H5OH(l) C2H5OH(g) ΔfH° (kJ/mol) -277.0 -235.3 S° (J/K⋅mol) 160.7 282.7 ΔfG° (kJ/mol) -174.7 -168.5

69 °C

65. The Ksp of silver bromide is 5.4 × 10−13 at 298 K. AgBr(s) Ag+(aq) + Br−(aq) What is ΔrG°? (R = 8.314 J/K⋅mol)

7.0 × 10^1 kJ/mol

11. Which of the following is the third law of thermodynamics as defined by Ludwig Boltzmann?

A perfect crystal at 0 K has zero entropy.

33. A flask containing helium gas is released into a closed room. Which of the following ideas concerning entropy is/are true?

All of these statements are true.

45. At what temperatures will a reaction be spontaneous if ΔrH° = +62.4 kJ and ΔrS° = +301 J/K?

All temperatures above 207 K

13. Which of the following linear chain alcohols is likely to have the highest standard entropy in the liquid state?

CH3CH2CH2CH2CH2OH

20. Which of the following compounds has the highest standard entropy per mole at 298 K?

CO(g)

16. Which of the following changes lead to a decrease in entropy?

Condensation of steam on glass

7. Which of the following is the first law of thermodynamics?

Energy cannot be created or destroyed.

8. Which of the following is the second law of thermodynamics?

In a spontaneous process, the entropy of the universe increases.

44. For a chemical reaction, if ΔrG° = 0, then _____.

K = 1

54. For which of the following substances is the standard free energy of formation not equal to zero at 298 K?

Mg(g)

18. In which of the following reactions is ΔrS° expected to be positive?

None of these

36. If ΔrG° > 0 for a reaction at all temperatures, then ΔrH° is _____ and ΔrS° is _____.

Positive; negative

43. Which of the following is true of a reaction that is product-favored?

Q < K and rG < 0

2. Which of the following statements concerning the spontaneity of chemical and physical changes is correct?

Spontaneous changes occur only in the direction that leads to equilibrium.

10. Which of the following statements concerning entropy is not correct?

The dispersal of matter, such as the spontaneous expansion of a gas, cannot be explained by an increase in entropy.

78. Which of the following statements about entropy is true?

The entropy of a substance will increase on going from a solid to a liquid to a gas.

46. At what temperatures will a reaction be spontaneous if ΔrH° = +117 kJ and ΔrS° = -35 J/K?

The reaction will never be spontaneous.

30. For the reaction given below, ΔH0 = −1516 kJ at 25°C and ΔS0 = −432.8 J/K at 25°C. This reaction is spontaneous _____. SiH4(g) + 2 O2(g) → SiO2(s) + 2 H2O

only below a certain temperature

57. Thermodynamics can be used to determine all of the following except _____.

the rate of reaction

59. For a chemical system, ΔrG° and ΔrG are equal when:

the reactants and products are in standard state conditions.

42. ΔG° = 0 for a reaction indicates that _____.

the reaction is at equilibrium

77. A reaction is said to be under thermodynamic control when _____.

thermodynamics is controlling the ratio of products

29. What is the sign of ΔH (system) and ΔS (system) if a chemical reaction is spontaneous only at lower temperatures under standard conditions?

ΔH (system) is negative, and ΔS (system) is negative.

34. When a real gas is compressed from low pressure to high pressure, its temperature increases. Which of the following is true for ΔH and ΔS?

ΔH < 0 and ΔS < 0

41. Which of the following is correct for the condensation of gaseous oxygen at -188 °C? (The normal boiling point of oxygen is -183 °C.)

ΔH < 0, ΔS < 0, and ΔG >0.

22. For the reaction Br2(l) → 2Br(g), _____.

ΔH is + and ΔS is +

32. A 100 mL sample of water is placed in a coffee cup calorimeter. When 1.0 g of an ionic solid is added, the temperature decreases from 21.5 °C to 20.8 °C as the solid dissolves. For the dissolving of the solid, _____.

ΔS(universe) > 0

21. Which of the following is true of the deposition of a gaseous substance?

ΔS° < 0 and ΔH° < 0.

40. If a chemical reaction is exothermic but not spontaneous, which of the following must be true?

ΔrG > 0, ΔrS < 0, and ΔrH < 0

38. While diluting concentrated sulfuric acid with water, the temperature of the solution increases rapidly. What are the signs of ΔrH, ΔrS, and ΔrG for the process?

ΔrH < 0, ΔrS > 0, and ΔrG < 0

35. Hydrogen gas is prepared by electrolysis of water according to the reaction below. 2 H2O() → 2 H2(g) + O2(g) Predict the signs of ΔrH and ΔrS.

ΔrH > 0 and ΔrS > 0

37. The dissolution of ammonium nitrate occurs spontaneously in water at 25 °C. As ammonium nitrate dissolves, the temperature of the water decreases. What are the signs of ΔrH, ΔrS, and ΔrG for this process?

ΔrH > 0, ΔrS > 0, and ΔrG < 0

39. If a cube of ice at 0 °C is placed outside on a warm summer day, the ice will melt spontaneously. What are the signs of ΔrH, ΔrS, and ΔrG for the process?

ΔrH > 0, ΔrS > 0, and ΔrG < 0