CHEM 341, Fall 2007 Name:___________________
Exam 3
The value of the gas constant R is 0.0820574 L atm mol-1 K-1, 1.98721 cal mol-1 K-1, and
8.31447 J mol-1 K-1. The atomic molar mass of H is 1.0079 g/mol; for C it is 12.01 g/mol;
for O it is 16.00 g/mol. 1 atm = 760 Torr; 1 dm3 = 1 L; 1 L = 1000 cm3; 1 m3 = 1000 L.
Answer all questions and show your working. Write clearly. No credit will be given for
illegible or ambiguous work.
A. Multiple choice (30 points)
1. _____ Given for aluminum that
T fusion = 933 K
∆fus H ° = 2538 cal mol-1
Cp,m (liquid) = 8.2 cal K-1 mol -1
Cp,m (solid) = 7.6 cal K-1 mol-1
Calculate the entropy change for aluminum when one mole of the metal is heated
from 873 K to 973 K.
A) 0.035 cal K-1 mol -1
B) 1.23 cal K-1 mol -1
C) 1.72 cal K-1 mol -1
D) 3.57 cal K-1 mol -1
E) -1.87 cal K-1 mol -1
2. _____ Consider the following reaction:
S2Cl2 (g) + 2 OCl2 (g) → 2 SOCl2 (g) + Cl2 (g)
Δf G° (kJ/mol) -32 97.9 -320 0.0
Δr G° for the reaction in kJ/mol is:
A) -804
B) -476
C) -386
D) -413
E) -799
3. _____ The value of Δf G° for Mg (g) is 113.10 kJ mol-1 at 298.15 K, and Δf H° for Mg (g) is
147.70 kJ mol-1 at the same temperature. Assuming that ΔfH° is constant in the
interval 250-400 K, calculate Δf G° for Mg (g) at 250 K.
A) 105.58 kJ mol-1
B) 142.11 kJ mol-1
C) 70.98 kJ mol-1
D) 163.33 kJ mol-1
E) 118.69 kJ mol-1
