chemistry - conversion rate

Question

Solid carbon (C) and water vapor (H2O) react to form gaseous carbon monoxide (CO) and dihydrogen gas (H2). The reaction is endothermic. In a closed system, an equilibrium mixture of the four substances is obtained. Which statement is correct?

A. If this mixture is cooled at a constant pressure, the conversion rate of water vapor will increase.

B. If this mixture is compressed at a constant temperature, the conversion rate of water vapor will decrease. C. The conversion rate of water vapor does not change when the mixture is cooled at a constant pressure.

D. The conversion rate of water vapor does not change when the mixture is compressed at a constant temperature.

The answer is B. PLease explain to me, why A,C, D are wrong and B is correct.

Answer 1

LeChatelier for T effect: Put energy into reaction as a reactant or product. Endothermic means the rxn looks like:

energy + C(s) + H₂O(g) ⇒ CO(g) + H₂(g)

Decreasing temperature reduces energy, so reaction will go to left in response. A and C wrong.

For total pressure effect, just look at total moles of gas on each side of the equilibrium. If pressure is decreased, the equilibrium will move towards increasing the moles of gas (countering the decrease of pressure). This will move equilibrium to the right (B correct, D wrong)