CHM110 MIDTERM TEST 2
There are 4 questions, worth 25 marks each. Only aids allowed are non-programmable
1. (25 marks)
a. Consider the van der Waal’s equation: (P + n2a/V2) (V-nb) = nRT
What is the term subtracted from the volume, why is it subtracted?
What is the term added to the pressure, why is it added?
b. At 500 Celsius, the equilibrium constant, Kc is 6.90 x 10-4 M-2 for the reaction
N2 + 3H2 2NH 3, all in the gaseous state
If the volume of the vessel containing the mixture at equilibrium is halved, but the temperature is
kept constant, in what direction will spontaneous reaction occur? Explain. What will happen to
the equilibrium constant? Explain.
2. (25 marks)
a. Briefly explain why diffusion rates are so much less than molecular velocities.
b. Why are effusion rates even less than diffusion rates?
c. The rate of effusion of a gaseous oxide of sulfur was measured to be 24.0 mL/min. Under the
same conditions, the rate of effusion of pure methane gas, CH4, was 47.8 mL/min. What is the
molar mass and the formula of the unknown gas?
Atomic masses (g/mol): H = 1.01, C = 12.01, O = 16.00, S = 32.07