# 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

#### Solution Summary

Fifteen thermodynamics problems (DeltaG - Gibbs Free Energy, DeltaS - Entropy, DeltaH - Enthalpy) are solved with full working and explanations. This is a great set of problems.