University of South Florida

CHM 2046

1)For a particular process ΔG is less than ΔH. Therefore

1. 1. ΔS is positive.
   2. ΔS is negative.
   3. ΔS is zero.
   4. ΔS is negative if ΔH is positive and ΔS is positive if ΔH is negative.

2. For a particular process, ΔG = ΔH at a given temperature and pressure. Therefore,
   1. ΔS is positive if ΔH is positive and negative is ΔH is negative.
   2. ΔS is negative if ΔH is positive and positive if ΔH is negative.
   3. ΔS is zero.
   4. ΔS = ΔG/T.

3. The solubility of manganese(II) fluoride in water is 6.6 g/mL at 40°C and 4.8 g/L at 100°C. Based on these data, what is the sign of ΔH° and ΔS° for the process below?

MnF2(s) ? Mn2+(aq) + 2 F-(aq)

1. 1. ΔH° is negative but the sign of ΔS° cannot be determined from this information.
   2. ΔH° is negative and ΔS° is definitely negative.
   3. ΔH° is positive but the sign of ΔS° cannot be determined from this information.
   4. ΔH° is positive and ΔS° is definitely negative.

4. At 25°C, ΔH° = 1.895 kJ and ΔS° = -3.363 J/K for the transition C(graphite) → C(diamond)

Based on these data

1. 1. graphite cannot be converted to diamond at 1 atm pressure.
   2. diamond is more stable than graphite at all temperatures at 1 atm.
   3. diamond is more stable than graphite below 290°C and graphite is more stable than diamond above 290°C.
   4. graphite is more stable than diamond below 290°C and diamond is more stable than graphite above 290°C.

5. For bromine, ΔH°vap = 30.91 kJ/mol and ΔS°vap = 93.23 JK-1mol-1 at 25°C. What is the normal boiling point for bromine?
   1. 25°C
   2. 58°C

C) 124°C

D) 332°C

6. Consider the reaction:

N2(g) + 3 F2(g) → 2 NF3(g) ΔH° = -249 kJ and ΔS° = -278 J/K at 25°C

Calculate ΔG° and state whether the equilibrium composition should favor reactants or products at standard conditions.

1. ΔG° = -332 kJ; the equilibrium composition should favor products.
2. ΔG° = -332 kJ; the equilibrium composition should favor reactants.
3. ΔG° = -166 kJ; the equilibrium composition should favor products.
4. ΔG° = -166 kJ; the equilibrium composition should favor reactants.

7. Which statement is true about the formation of CaCO3(s) from CaO(s) and CO2(g) at 1.00 atm?

CaO(s) + CO2(g) → CaCO3(s)                      ΔH° = -178.7 kJ and ΔS° = -150.4 J/K

1. 1. The reaction is spontaneous at all temperatures.
   2. The reaction is spontaneous at high temperatures.
   3. The reaction is spontaneous at low temperatures.
   4. The reaction is not spontaneous at any temperature.

8. The signs of ΔG, ΔH, and ΔS at 25°C are shown below for three reactions.

Which reaction could go in the reverse direction at high temperature?

1. 1. I
   2. II
   3. III
   4. I and II

9. For the evaporation of water during perspiration on a hot, dry day,
   1. ΔH is positive and TΔS = ΔH.
   2. ΔH is positive and TΔS > ΔH.
   3. ΔH is positive and TΔS < ΔH.
   4. ΔH is negative and TΔS is positive.

10. For the reaction below ?G° = + 33.0 kJ, ?H° = + 92.2 kJ, and ?S° = + 198.7 J/K. Estimate the temperature at which this reaction becomes spontaneous.

2 NH3(g) → N2(g) + 3 H2(g) A) 0.464 K

2. 166 K
3. 298 K
4. 464 K

11. Calculate the standard free energy change at 25°C for the reaction 2 NO(g) + O2(g) → 2 NO2(g).

1. 1. -4.7 kJ

B) -72.6 kJ

C) -157.8 kJ

D) -532.6 kJ

12. For any thermodynamic function Y, ΔY° for a reaction refers to the change in Y for the process in which
    1. the mixed reactants at 1 atm go to equilibrium at 1 atm.
    2. the separate reactants at 1 atm go to equilibrium at 1 atm.
    3. the separate reactants in their standard states are completely converted to separate products in their standard states.
    4. the spontaneous reaction occurs.

13. Which of the following is true?
    1. As a reaction at constant temperature and pressure goes to equilibrium, |ΔG| decreases.
    2. The larger ΔG°, the faster the reaction.
    3. The standard state for solutes is the pure solute at 1 atm.
    4. When a reaction reaches equilibrium, ΔG° = 0.

14. Which statement is true concerning the standard states of F2(g) and C6H12O6(aq)?
    1. The standard state for F2(g) is the pure gas at 1 atm and for C6H12O6(aq) is the pure solid at 1 atm.
    2. The standard state for F2(g) is the pure gas at 1 mol/L and for C6H12O6(aq) is the pure solid at 1 atm.
    3. The standard state for F2(g) is the pure gas at 1 atm and for C6H12O6(aq) is the solution at a concentration of 1 mol/L.
    4. The standard state for F2(g) is the pure gas at 1 mol/L and for C6H12O6(aq) is the solution at a concentration of 1 mol/L.

15. Calculate the standard free energy for the reaction given. 2 CH3OH(l) + 3 O2(g) → 2 CO2(g) + 4 H2O(l)

A) -465.2 kJ

B) -797.8 kJ

C) -1404.8 kJ

D) -2069.8 kJ

16. Which is the lowest at 25°C?
    1. ΔG°f for H2O (s)
    2. ΔG°f for H2O (l)
    3. ΔG°f for H2O (g)
    4. 1/2ΔG°f for O2 (g) plus ΔG°f for H2O (g)

17. Which of the following is zero at 25°C?
    1. ΔG°f for N2(g)
    2. ΔG°f for H2O (l)
    3. S° for N2 (g)
    4. S° for H2O (l)

18. A positive value of ΔG°f for a solid compound at 25°C means the
    1. compound cannot exist at 25°C and 1 atm.
    2. compound must be a liquid or a gas at 25°C and 1 atm.
    3. process of forming the compound from the elements is exothermic.
    4. process of forming the compound from the stable elements at 25°C and 1 atm is nonspontaneous.

19. At 25°C, ΔG°f is -620 kJ/mol for SiCl4(g) and -592 kJ/mol for MgCl2(s). Calculate ΔG° for the reaction,

    

      and determine if the reaction is spontaneous at 25°C if the pressure of SiCl4(g) is 1 atm.
    1. ΔG° = 28 kJ; the process is spontaneous.
    2. ΔG° = 28 kJ; the process is nonspontaneous.
    3. ΔG° = -564 kJ; the process is spontaneous.
    4. ΔG° = -564 kJ; the process is nonspontaneous.

20. Which of the following are unstable with respect to their constituent elements at 25°C?

1. 1. C8H18(l), CH3OH(l)

B) C8H18(l), C2H2(g)

3. C2H2(g)
4. CH3OH(l)

21. In general, as a reaction goes to equilibrium
    1. ΔG decreases.
    2. ΔG°f decreases.
    3. ΔG goes to zero.
    4. ΔG° decreases.

22. At 25°C, ΔG° = -198 kJ for the reaction, NO(g) + O3(g) ? NO2(g) + O2(g). Calculate ΔG under the following conditions:

1. 1. -159 kJ
   2. -167 kJ
   3. -198 kJ
   4. -236 kJ

23. For a reaction at constant temperature, as Q increases
    1. ΔG and ΔG° increase.
    2. ΔG and ΔG° decrease.
    3. ΔG increases, but ΔG° remains constant.
    4. ΔG decreases, but ΔG° remains constant.

24. At high temperatures boron carbide vaporizes according to the equation B4C(s) ? 4 B(g) + C(s)

Which equation describes the relationship between ΔG° and ΔG for this reaction?

1. 1. ΔG = ΔG° + R T ln (pB ? [C]/[B4C])
   2. ΔG = ΔG° + R T ln pB
   3. ΔG = ΔG° + 4 R T ln pB
   4. ΔG = ΔG° - 4 R T ln pB

25. At 2600 K, ΔG° = 775 kJ for the vaporization of boron carbide: B4C(s) ? 4 B(g) + C(s)

Find ΔG and determine if the process is spontaneous if the reaction vessel contains 4.00 mol B4C(s), 0.400 mol of C(s), and B(g) at a partial pressure of 1.0 × 10-5 atm. At this temperature, R T = 21.6 kJ.

1. 1. ΔG = -270 kJ; spontaneous.
   2. ΔG = -270 kJ; nonspontaneous.
   3. ΔG = -220 kJ; spontaneous.
   4. ΔG = -220 kJ; nonspontaneous.

26. ΔG = ΔG° for a reaction
    1. if Q = K.
    2. if Q = 1.
    3. at STP.
    4. at the start of the reaction.

27. What is the relationship between ΔG and the ΔG°F for the reaction below? MgF2(s) → Mg2+(aq) + 2 F-(aq)

A) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F- (aq)] - ΔG°f [MgF2 (s)]} + RT ln ([Mg2+] [F-]2/ [MgF2])

B) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F- (aq)] - ΔG°f [MgF2 (s)]} + RT ln ([Mg2+] [F-])2)

C) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F- (aq)]} + RT ln ([Mg2+] [F-]2)

D) ΔG = {ΔG°f [Mg2+ (aq)] + 2 ΔG°f [F- (aq)] - ΔG°f [MgF2 (s)]} + RT ln Ksp

28. If Q increases
    1. ΔG increases and the reaction becomes more spontaneous.
    2. ΔG increases and the reaction becomes less spontaneous.
    3. ΔG decreases and the reaction becomes more spontaneous.
    4. ΔG decreases and the reaction becomes less spontaneous.

29. What is the relationship between ΔG, Qp, and Kp for a reaction involving gases?
    1. ΔG = Qp/Kp
    2. ΔG = Kp/Qp
    3. ΔG = RTln(Qp/Kp)
    4. ΔG = RTln(Kp/Qp)

30. When equilibrium is reached at constant temperature and pressure,
    1. Q = 1.
    2. ΔG° = 0.
    3. S is maximized.
    4. G is minimized.

31. Calculate Ksp for PbI2 at 25°C based on the following data:

A) 4 × 10-31

B) 8 × 10-18

C) 9 × 10-9

D) 5 × 10-5

32. At high temperatures, boron carbide vaporizes according to B4C(s) ? 4 B(g) + C(s)

1. 1. 832 kJ
   2. 799 kJ
   3. 281 kJ
   4. 247 kJ

33. Solid NaHCO3 is heated to 90°C. At equilibrium the total pressure of the gases produced is

0.545 atm. Calculate ΔG° at 90°C for the reaction

2 NaHCO3(s) ? Na2CO3(s) + H2O(g) + CO2(g).

A) -7.85 kJ

B) -3.67 kJ

C) +3.67 kJ

D) +7.85 kJ

34. What is K if ΔG° = -18.0 kJ for a reaction at 25°? A) 1.4 × 103

B) 1.2 × 102

C) 8.1 × 10-3

D) 7.3 × 10-4

35. If ΔG° is negative for a reaction,
    1. K < 0.
    2. K = 0.
    3. K is between 0 and 1.
    4. K > 1.

36. If ΔG° is positive for a reaction,
    1. K < 0.
    2. K = 0.
    3. K is between 0 and 1.
    4. K > 1.

37. For the following reaction find Kp at 25°C and indicate whether Kp should increase or decrease as the temperature rises.

NH4HS(s) ? H2S(g) + NH3(g)ΔH° = 83.47 kJ and ΔG° = 17.5 kJ at 25°C.

1. 1. Kp = 8.6 × 10-4 and Kp should increase as the temperature rises.
   2. Kp = 8.6 × 10-4 and Kp should decrease as the temperature rises.
   3. Kp = 1.2 × 103 and Kp should increase as the temperature rises.
   4. Kp = 1.2 × 103 and Kp should decrease as the temperature rises.

38. If ΔG is small and positive,
    1. the forward reaction is spontaneous and the system is far from equilibrium.
    2. the forward reaction is spontaneous and the system is near equilibrium.
    3. the reverse reaction is spontaneous and the system is far from equilibrium.
    4. the reverse reaction is spontaneous and the system is near equilibrium.

39. In figure (1) below argon atoms, represented by unshaded spheres, and neon atoms, represented by shaded spheres, are in separate compartments. Figure (2) shows the equilibrium state of the system after the stopcock separating the two compartments is opened. Assuming that argon and neon behave as ideal gases, what are the signs (+, -, or 0) of ΔH, ΔS, and ΔG for this process?

1. 1. ΔH = +, ΔS = -, ΔG = +
   2. ΔH = 0, ΔS = +, ΔG = -
   3. ΔH = 0, ΔS = -, ΔG = +
   4. ΔH = -, ΔS = +, ΔG = -

40. In figure (1) below oxygen molecules, represented by unshaded spheres, and chlorine molecules, represented by shaded spheres, are in separate compartments. Figure (2) shows the equilibrium state of the system after the stopcock separating the two compartments is opened. Assuming the oxygen and the chlorine behave as ideal gases, what are the signs (+, -, or 0) of ΔH, ΔS, and ΔG for this process?

1. 1. ΔH = +, ΔS = -, ΔG = +
   2. ΔH = 0, ΔS = +, ΔG = -
   3. ΔH = 0, ΔS = -, ΔG = +
   4. ΔH = -, ΔS = +, ΔG = -

41. The figure represents the spontaneous deposition of iodine in which iodine vapor, I2(g), becomes crystalline iodine solid I2(s): I2(g): → I2(s). What are the signs (+ or -) of ΔH, ΔS, and ΔG for this process?

1. 1. ΔH = +, ΔS = +, ΔG = +
   2. ΔH = +, ΔS = +, ΔG = -
   3. ΔH = -, ΔS = -, ΔG = +
   4. ΔH = -, ΔS = -, ΔG = -

42. The figure represents the spontaneous evaporation of nitrogen in which liquid nitrogen, N2(l), becomes gaseous nitrogen, N2(g): N2(l) → N2(g). What are the signs (+ or -) of ΔH, ΔS, and ΔG for this process?

1. 1. ΔH = +, ΔS = +, ΔG = +
   2. ΔH = +, ΔS = +, ΔG = -
   3. ΔH = -, ΔS = -, ΔG = +
   4. ΔH = -, ΔS = -, ΔG = -

43. An ideal gas is expanded at constant temperature. What are the signs (+, -, or 0) of ΔH, ΔS, and ΔG for this system?

1. 1. ΔH = +, ΔS = -, ΔG = +
   2. ΔH = 0, ΔS = +, ΔG = -
   3. ΔH = 0, ΔS = -, ΔG = +
   4. ΔH = -, ΔS = +, ΔG = -

44. The figure above represents the nonspontaneous reaction O2(g) → 2O(g). What are the signs (+ or -) of ΔH, ΔS, and ΔG for this process?
    1. ΔH = +, ΔS = +, ΔG = +
    2. ΔH = +, ΔS = +, ΔG = -
    3. ΔH = -, ΔS = -, ΔG = +
    4. ΔH = -, ΔS = -, ΔG = -

45. The figure above represents the reaction O2(g) → 2O(g), which is nonspontaneous at 25°C. How will the spontaneity of this reaction vary with temperature? This reaction is
    1. nonspontaneous at all temperatures.
    2. nonspontaneous at high temperatures and spontaneous at low temperatures.
    3. spontaneous at high temperatures and nonspontaneous at low temperatures.
    4. spontaneous at all temperatures.

The figure below represents the spontaneous reaction of H2 (shaded spheres) with O2 (unshaded spheres) to produce gaseous H2O.

46. What are the signs (+, or -) of ΔH, ΔS, and ΔG for this process?
    1. ΔH = +, ΔS = +, ΔG = +
    2. ΔH = +, ΔS = +, ΔG = -
    3. ΔH = -, ΔS = -, ΔG = +
    4. ΔH = -, ΔS = -,ΔG = -

47. How will the spontaneity of this reaction vary with temperature? This reaction is
    1. nonspontaneous at all temperatures.
    2. nonspontaneous at high temperatures and spontaneous at low temperatures.
    3. spontaneous at high temperatures and nonspontaneous at low temperatures.
    4. spontaneous at all temperatures.

Consider the reaction 2A(g) ? A2(g). The following pictures represent two possible initial states and the equilibrium state of the system.

48. For initial state 1 what is the relationship between the reaction quotient, Qp, and the equilibrium constant, Kp?
    1. Qp < Kp
    2. Qp = Kp = 1
    3. Qp = Kp ≠ 1
    4. Qp > Kp

49. For initial state 2 what is the relationship between the reaction quotient, Qp, and the equilibrium constant, Kp?
    1. Qp < Kp
    2. Qp = Kp = 1
    3. Qp = Kp ≠ 1
    4. Qp > Kp

50. What are the signs (+ or -) of ΔH, ΔS, and ΔG when the system spontaneously goes from initial state 1 to the equilibrium state?

1. ΔH = +, ΔS = +, ΔG = +
2. ΔH = +, ΔS = +, ΔG = -
3. ΔH = -, ΔS = -, ΔG = +
4. ΔH = -, ΔS = -, ΔG = -

51. What are the signs (+ or -) of ΔH, ΔS, and ΔG when the system spontaneously goes from initial state 2 to the equilibrium state?

1. ΔH = +, ΔS = +, ΔG = +
2. ΔH = +, ΔS = +, ΔG = -
3. ΔH = -, ΔS = -, ΔG = +
4. ΔH = -, ΔS = -, ΔG = -

Consider the following gas-phase reaction of A2 (shaded spheres) and B2 (unshaded spheres): A2(g) + B2(g) ? 2 AB(g)                                 ΔG ° = +25 kJ

52. Which of the above reaction mixtures has the least spontaneous forward reaction? A) (1)

B) (2)

C) (3)

D) (4)

53. Which of the above reaction mixtures has the most spontaneous forward reaction? A) (1)

B) (2)

C) (3)

D) (4)

54. Which of the above reaction mixtures is ΔG of reaction = ΔG ° ? A) (1)

B) (2)

C) (3)

D) (4)

55. According to the diagram above, the forward reaction is

1. nonspontaneous at d and e, and spontaneous at f.
2. nonspontaneous at d, at equilibrium at e, and spontaneous at f.
3. spontaneous at d, at equilibrium at e, and nonspontaneous at f.
4. spontaneous at d, e, and f.

56. According to the diagram above,

1. ΔG° is positive and the equilibrium composition is rich in products.
2. ΔG° is positive and the equilibrium composition is rich in reactants.
3. ΔG° is negative and the equilibrium composition is rich in products.
4. ΔG° is negative and the equilibrium composition is rich is reactants.