Question

Study the reaction.
2A(?) + B(g) ⇌ A2B(g)

Both B and A2B are gases. When the reaction vessel is compressed, the equilibrium position does not change.

What conclusion can we draw about the state of “A” from this data?
A. "A" must be a gas because, if it were not, the equilibrium would shift toward the liquid or solid to relieve the pressure
B. "A" cannot be a gas because two gases cannot interact with each other due to assumptions of the ideal gas law
C. "A" must be a gas because only gases can react with other gases: the forward reaction would not occur otherwise
D. "A" cannot be a gas because, if it were, the equilibrium would shift toward the products to relieve the pressure.
C?

Answer 1

Nope, not C. If A were a gas, then compressing would affect the left side (more gasses) shifting the reaction to the product side.

Answer 2

C is incorrect

increasing pressure does not shift the equilibrium, so the gas volumes are equal on both sides of the equation ... B and A2B
... if A were a gas, the volumes would not be equal