Dr. Rogers
Thermodynamic Homework
Chem 112
1. What is the sign of the entropy change for each of the following processes? The system appears in bold
and is underlined. Your answer should be either (+) or (-)
A.
B.
C.
D.
E.
F.
G.
H.
Iodine sublimes
Ethyl alcohol condenses in a flask
Hydrogen and oxygen combine to form water
An artisan makes a pattern from yarn
Wood and oxygen are burned to provide heat
Water evaporates
Molten gold freezes
Butter melts
2. Which of the following reactions will have a
A.
B.
C.
D.
S < 0? You must select all of the correct answers.
CaO(s) + H2O(l)  Ca(OH)2(s)
NH3(g) + HCl(g)  NH4Cl(s)
Br2(g) + 3Cl2(g)  2BrCl3(g)
I2(s)  I2(g)
3. Which of the following reactions (equations unbalanced) would be expected to be spontaneous at 25 oC
and 1 atm?
A. Al2O3(s) + Fe(s)  Fe2O3(s) + Al(s)
B. PbO(s) + NH3(g)  Pb(s) + N2(g) + H2O(g)
C. 2CH4(g)  C2H6(g) + H2(g)
4. Which of the following has the largest entropy at 298 K?
A. Xe(g)
B. Ne(g)
C. Kr(g)
D. He(g)
E.
Ar(g)
5. Which of the following has the largest entropy at 298 K?
A. CH3Cl(g)
B. CH3Cl(l)
C. CCl4(g)
D. CH4(g)
E. CCl4(l)
6. Which of the following reactions has the largest positive molar entropy change?
A)
B)
C)
D)
E)
PCl5(g)  PCl3(g) + Cl2(g)
N2(g) + 3H2(g)  2NH3(g)
KClO4(s) + 4C(s)  KCl(s) + 4CO(g)
H2O(s)  H2O(g)
CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)
7. If the enthalpy of fusion of water at its normal melting point is 6.00 kJ/ mol, calculate S° for freezing 1.0
mole of water at this temperature.
8. The enthalpy of vaporization of ethanol, C2H5OH, is 38.7 kJ/ mol at its normal boiling point, 78°C. Calculate
S° for vaporization of 1 mole of ethanol at its normal boiling point.
9. For the melting of aluminum, Al(s)  Al(l),
melting point of Al in Kelvin.
Ho = 10.0 kJ/ mol and
So = 9.50 J/mol· K. Calculate the
10. The heat of vaporization of mercury is 60.7 KJ/ mol. For Hg(l), S = 76 J/mol K and for Hg(g) S = 175 J/ mol
K. Estimate the normal boiling point of liquid mercury.
11. What is the normal boiling point of nitromethane (CH3NO2) in Kelvin.
CH3NO2 (l)
CH3NO2 (g)
H = -113.1 kJ/mol
H = -74.73 kJ/mol
S = 171.76 J/mol K
S = 274.42 J/mol K
12. Given the following data, what is the G for this reaction at 298 K and is it spontaneous or
nonspontaneous?
2SO2(g) + O2(g)  2SO3(g)
G
(kJ/ mol–1)
–301
–372
13. A reaction is spontaneous at all temperatures if
A.
B.
C.
D.
H and S are both positive.
H and S are both negative.
H is positive and S is negative.
H is negative and S is positive.
14. Use the thermodynamic data in appendix D to Calculate G in KJ for the following reaction to determine if
it is spontaneous or not.
CO(g) +Cl2(g)  COCl2(g)
COCl2 (g) H = -204.6 kJ/mol
15. Which of the following conditions will result in a spontaneous reaction at all temperatures?
A) H > 0, S < 0
B) H > 0, S = 0
C) H < 0, S < 0
D) H > 0, S > 0
E) H < 0, S > 0
16. Calculate Gr° for the decomposition of ammonium nitrate at 298 K.
NH4NO3(s) → N2O(g) +
2H2O(l)
Hf°, kJ/ mol
–365.56
82.05
–285.83
S°, J/ mol· K
151.08
219.85
69.91
17. Calculate Gr° for the decomposition of mercury(II) oxide at 298 K.
2HgO(s)
→ 2Hg(l) +
O2(g)
Hf°, kJ/ mol
–90.83
S°, J/ mol ·K
70.29
76.02
205.14
18. For a reaction, Hr° = –92 kJ and Sr° = –65 J/K. Calculate the value of Gr° for this reaction at 25°C.
19. For the following reaction: CuO(s) + H2(g) → Cu(s) + H2O(g)
at 298 K, Hr° = –87.0 kJ and Sr° = 47.0 J/ K. Calculate Gr° at 400 K.
20. For the following reaction: C6H6(g) + 3H2(g) → C6H12(g)
at 298 K, Hr° = –206 kJ and Sr° = –363 J/K. Calculate Gr° at 500°C.
21. For the reaction : 2NH3(g) → 3H2(g) + N2(g)
Hr° = 92.22 kJ and Sr° = 198.75 J/K at 298 K. At what temperatures will this reaction will be
spontaneous with all reactants and products in their standard states,
22. What is the sign of the standard free energy change at low temperatures and at high temperatures for the
decomposition of phosgene? (Use thermodynamic data in appendix D if necessary)
COCl2(g) → CO(g) + Cl2(g)
23. For the reaction: 2H2(g) + CO(g) → CH3OH(l)
Hr° = –128.13 kJ and Sr° = –332.23 J/K at 298. Calculate Gr° at 100°C.
24. Using thermodynamic values from appendix D calculate G in KJ for the following reaction at 370 K
BaO(s) + CO2(g) → BaCO3(s)
25. Calculate Gr at 298 K for the reaction: C2H5OH(l) → C2H5OH(g, 0.0263 atm)
given Gr° = 6.2 kJ at 298 K.
+
–
26. Consider the reaction: NH3(aq) + H2O(l) 
 NH4 (aq) + OH (aq)
If Kc = 1.75 x 10–5 at 25°C, calculate Gr° for this reaction.
27. Calculate the equilibrium constant at 298 K for the reaction below.
NH3(g) +
HCl(g) → NH4Cl(s)
Gf°, kJ/ mol
–16.45
–95.30
–202.87
28. Calculate Gr for the following reaction at 298 K.
Ag(NH3)2+(aq, 0.100 M) → Ag+(aq, 0.00100 M) + 2NH3(aq, 0.00200 M)
Gr° = –41.0 kJ for this reaction at 298 K.
29. If Ksp of AgBr is 7.7 x 10–13 at 298 K, calculate Gr for the reaction of 5 mL of 0.20 M AgNO3(aq) with 5 mL of
0.20 M NaBr(aq) at 298 K.
30. If Gr° = 27.1 kJ at 25°C for the reaction: CH3COOH(aq) + H2O(l)
calculate Ka for this reaction at 298 K.


CH3COO–(aq) + H3O+(aq)
2+
31. At 304.8 K, G = -8.686 KJ for the reaction ZnF2(s) 
 Zn (aq) + 2F (aq).
A. Calculate the change in free energy, in KJ at the same temperature when [Zn2+] = 3.5 x 10-2 M and [F-]
= 2.3 x 10-3 M. (You may need to use thermodynamic data from appendix D)
B. Is the forward or reverse reaction spontaneous?
32. State how increasing the temperature influences the value of the equilibrium constant for each of the
following reactions.
A. N2O4(g) 
 2NO2(g)
B. 2 CO(g) + O2(g) 
 2CO2(g)
C. 2HI(g) 
H
(g)
+
I
2
2(g)


D. C(s) + H2O(g)  CO(g) + H2(g)
33. Consider the phase diagram of a pure compound. Which statement applies?
C
A
B
temperature
A. The path A  C represents sublimation.
B. Following the path A  B  C the compound would first liquefy and then
vaporize.
C. If the compound is in state A, continued reduction of the pressure (at constant
temperature) will cause it to melt.
D. None of these statements is correct.
34. In a phase diagram what does the triple point represent?
35. In the phase diagram, which transition represents the condensation of a gas to a liquid?
A
B
P
C
D
T
(A) B to A (B) D to B (C) C to D (D) A to D
Answers:
1. A (+) B (-) C (-) D (-) E (+) F (+) G (-) H (+)
2. A B C
3. B
4. A
5. C
6. C
7. –22.0 J/ K
8. 110 J/K
9. 1050 K
10. 614 K
11. 373 K
12. –142 kJ; spontaneous
13. D
14. -67.43 KJ; spontaneous
15. E
16. –186.21 kJ
17. +117.1 kJ
18. –73 kJ
19. –106 kJ
20. +74.6 kJ
21. at temperatures above 464 K.
22. high temp G = (-); low temp G = (+)
23. –4.21 kJ
24. -205.6 KJ
25. –2.8 kJ
26. 27.1 kJ
27. 9.39 x 1015
28. –83.2 kJ
29. 57.7 kJ
30. 1.78 x 10–5
31. A. -47.9 KJ B. forward
32. A. Increase; B Decrease; C increase; D increase
33. D
34. the pressure and temperature at which all three phases of a
substance can co-exist
35. B