Practice Problems for Chapter 17
1. Which of these species would you expect to have the lowest standard entropy (S°)?
a. Br2(l) or Br2 (g)
b. Cl2(g) or 2Cl(g)
c. F2(g) at 1 atm or F2 (g) at 2 atm
d. H2O(l) at 25C or H2O(l) at 45C
e. O2 at 298 K or O3 at 298K
2. Predict the sign of ΔS for the following processes:
a. Sublimation of Naphthalene
b. sugar dissolving in water
c. Ag+(aq) + Cl-(aq)  AgCl(s)
d. H+(aq) + OH-(aq)  H2O(l)
e. 4 NH3 (g) + 3O2 (g)  2 N2 (g) + 6 H2O (l)
3. Calculate ΔS°, ΔH° and ΔG° at 298 K for the following reaction using the
thermodynamic data provided below.
2 CsCl(aq) + H2SO4(aq)  Cs2SO4(aq) + 2HCl(aq)
S°(J/K·mol)
Hf (kJ/mol)
CsCl(aq)
188
-415
H2SO4(aq)
17.2
-908
HCl(aq)
56.5
-167
Cs2SO4(aq)
283
-1400
4. Hydrogen peroxide (H2O2) decomposes according to the equation
H2O2(l) → H2O(l) + 1/2O2(g).
Calculate K for this reaction at 25°C given that ΔH° = –98.2 kJ/mol, ΔS° = 70.1 J/K·mol.
5. The equilibrium constant at 427°C for the reaction N2(g) + 3H2(g)  2NH3(g) is
Kp = 9.4 × 10–5.
a. Calculate the value of ΔG° for the reaction under these conditions.
b. Calculate the free energy change for the reaction when the partial pressures are 3.00
atm for N2, 2.00 atm for H2 and 6.00 atm for NH3.
c. Is the reaction spontaneous under these conditions?
6.a. ΔG° at 298 K for the following reaction using the thermodynamic data provided
below.
ZnCl2(aq) + H2SO4(aq)  ZnSO4(aq) + 2HCl(aq)
ZnCl2 (aq)
H2SO4(aq)
HCl(aq)
ZnSO4(aq)
Gf (kJ/mol)
-410
-742
-131
-892
b. Calculate the equilibrium constant K for the reaction at this temperature.
7. Specify if the following statements are true or false?
a. Hf = 0 for I2(g)
b. Gf = 0 for F2(g)
c. S = 0 for diamond at any Temperature
d. All exothermic reactions are spontaneous
e. At equilibrium, ΔG° = 0