MCAT Question A Day - 4/3/14 - Answer!
For the reaction 2NO2(g)→ N2O4(g), which of the following is true?
I. Removing NO2 shifts the equilibrium to the left.
II. Increasing the volume of the container shifts the equilibrium to the right.
III. Adding helium gas to the container shifts the equilibrium to the right.
A. I only
B. II only
C. III only
D. I and II only
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The correct answer is (A). The reaction shifts to the left in response to the loss of NO2. Increasing the volume has the reverse effect from that stated in II—there’s more room for the more numerous NO2’s. Adding an inert gas raises the total pressure, but only partial pressures of reactants and products figure into the equilibrium expression, so the equilibrium will not shift in III.
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