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 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

Looking at the balanced equation which is endothermic, we have ...

C(s) + H₂O(g) + heat ==> CO(g) + H₂(g)

A. is incorrect because since the rxn is endothermic, cooling the mixture at equilibrium will shift the reaction to the left in accordance with Le Chatelier's principle, so the conversion rate of H2O will DECREASE, not increase.

B. is correct because there are more mols of gas on the product (right) side than on the reactant (left) side and therefore compressing (increasing the pressure) will shift the equilibrium to the left according to Le Chatelier. Thus, the conversion rate of H2O will indeed decrease.

C. is incorrect because the conversion rate of H2O will DECREASE when the system is cooled since it is endothermic.

D. is incorrect as explained above in (A), the conversion rate of H2O will decrease when the system is compressed.