CHEM 341, Fall 2007 Name:___________________
Exam 2
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) 250.0 g of hot coffee at 95.0 °C are placed in a 0.2000 kg mug at 20.0 °C. The specific
heat of the coffee is 4.00 J/g °C, while that of the mug is 0.80 J/g °C. Assuming no heat
is lost to the surroundings, what is the final temperature of the system: mug + coffee?
A) 61.7 °C
B) 117 °C
C) 76.0 °C
D) 84.7 °C
E) 57.5 °C
_____ (2) The complete combustion of propane, C3H8 (g), is represented by the equation:
C3H8 (g) + 5 O2 (g) → 3 CO2 (g) + 4 H2O (l) Δc H° = -2220 kJ/mol
How much heat is evolved in the complete combustion of 20.0 L C3H8 (g) at STP?
A) 2486 kJ
B) 495 kJ
C) 994 kJ
D) 1007 kJ
E) 1981 kJ
_____ (3) Some “beetles” defend themselves by spraying hot quinine, C6H4O2 (l), at their enemies.
Calculate Δr H° for this reaction.:
C6H4(OH)2 (l) + H2O2 (l) → C6H4O2 (l) + 2 H2O (l)
Given: C6H4(OH)2 (l) → C6H4O2 (l) + H2 (g) Δr H° = 177 kJ/mol
The standard enthalpies of formation of H2O2 (l) and H2O (l) are -187.8 and -285.8
kJ/mol, respectively.
A) -561.6 kJ/mol
B) -384.2 kJ/mol
C) -206.8 kJ/mol
D) +79.00 kJ/mol
E) none of these
_____ (4) Calculate Δf H° of octane, C8H18 (l), given the enthalpy of combustion of octane to CO2
(g) and H2O (l), -5471 kJ/mol, and the standard enthalpies of formation of CO2 (g) and
H2O (l), -393.5 kJ/mol and -285.8 kJ/mol, respectively.
A) +4792 kJ/mol
B) -249.2 kJ/mol
C) +249.2 kJ/mol
D) -4792 kJ/mol
E) none of these
