15 Thermodynamics Problems (Delta G, Delta S, Delta H)

1) From the following Ho and So values predict which of reactions I, II, and III would be spontaneous at 300ºC.

H (kJ)
S(J/K)

I
-5.0
-15

II
-10.0
+20

III
-5.0
-30

A. I
B. II
C. III
D. I and II
E. II and III

2) From the following Ho and So values predict which of reactions I, II, and III would be spontaneous at 25ºC.

H (kJ)
S(J/K)

I
+10.5
+30

II
+1.8
-113

III
-126
+84

A. I
B. II
C. III
D. I and II
E. II and III

3) Calculate the entropy change (J/mole.K) of the reaction. The molar entropies [S] are given in brackets after each substance.

2 CuS(s) [66.5] + 3 O2(g) [205.1]" 2 CuO(s) [42.6] + 2 SO2(g) [248.2]

A. -114.2
B. -139.1
C. +33.0
D. +68.2
E. +166.7

4) Calculate the entropy change (J/mole.K) of the reaction. The molar entropies [S] are given in brackets after each substance.

3 NO2(g) [240.1] + H2O(l) [69.9] --> 2 HNO3(aq) [146.4] + NO(g) [210.8]

A. -286.6
B. -212.4
C. -156.3
D. +47.2
E. +156.3

5) Given Sº = -266.3 and the listed [Sº values] calculate Sº for Fe3O4(s).

4 Fe3O4(s) [____] + O2(g) [205.1] ---> 6 Fe2O3(s) [87.4]

A. +111.1
B. +122.4
C. +134.1
D. +146.4
E. +159.6

6. Given Sº = -114.3 and the listed [Sº values] calculate Sº for CCl4(g).

CH4(g) [186.3] + 4 Cl2(g) [223.0] ---> CCl4(g) [____] + 4 HCl(g) [186.9]

A. +150.6

B. +175.6

C. +216.4

D. +195

E. +240.5

7. Predict which of the following reactions has a negative entropy change.

I. 2 SO2(g) + O2(g) --> 2 SO3(g)

II. MgO(s) + CO2(g) --> MgCO3(s)

III. PCl5(s) --> PCl3(l) + Cl2(g)

A. I

B. II

C. III

D. I and II
E. II and III

8) Predict which of the following reactions has a positive entropy change.

I. Ag+(aq) + Cl-(aq) --> AgCl(s)

II. NH4Cl(s) --> NH3(g) + HCl(g)

III. 2 NH3(g) --> N2(g) + 3 H2(g)

A. I
B. II
C. III
D. I and II
E. II and III

9) The enthalpy and entropy change of a reaction are -6.1 kJ/mole and +38.9 J/mole K respectively at 25ºC. What is the free energy change in kJ/mole?

A. -17.7
B. -11.6
C. -5.5
D. +5.5
E. +17.7

10) The enthalpy and entropy change of a reaction are -26.1 kJ/mole and +3.89 J/mole K respectively at 25ºC. What is the free energy change in kJ/mole?

A. -30.3
B. -27.3
C. -24.9
D. -17.3
E. +24.9

11) Using the listed information calculate Kp at 25ºC.

Ag2O(s) --> 2 Ag(s) + 1/2 O2(g)

Hºf (kJ/mole) -31.0, 0.0, 0.0

Sº (J/K.mole) 121.3, 42.6, 205.1

A. 2.22 x 10-3
B. 3.41 x 10-2
C. 2.22 x 10-2
D. 1.09 x 10-2
E. 4.41 x 10-1

12) Nitrosyl chloride decomposes by the following reaction with Hº = -51.7 kJ/mole and Sº = 48.2 J/mole.K. Estimate Kp at 100ºC.

NOCl(g) --> 1/2 N2(g) + 1/2 O2(g) + 1/2 Cl2(g)

A. 6.21 x 107
B. 2.48 x 108
C. 7.45 x 108
D. 3.25 x 109
E. 5.67 x 109

13) Using the listed information calculate the temperature (C) where Kp = 1.0.

Ag2O(s) --> 2 Ag(s) + 1/2 O2(g)

Hºf (kJ/mole) -31.0, 0.0, 0.0

Sº (J/K.mole) 121.3, 42.6, 205.1

A. 152
B. 194
C. 222
D. 367
E. 441

14) Using the listed [DGºf values] calculate DG for the reaction:

4 NH3(g) [-16.5] + 5 O2(g) [0.0] --> 4 NO(g) [+86.6] + 6 H2O(g) [-228.6]

A. -1091.2
B. -959.2
C. -878.8
D. -438.4
E. -125.5

15) Using the listed [[DGºf values] calculate DG for the reaction:

4 FeS2(s) [-166.7] + 11 O2(g) [0.0] --> 2 Fe2O3(s) [-740.9] + 8 SO2(g) [-300.3]

A. -3217.4
B. -2464.5
C. -1884.5
D. -1207.9
E. -874.5