JAMB Chemistry 2019 Paper

Concept:A decrease in pressure favours the side of an equilibrium with more gaseous moles.Explanation:Only gases are affected by pressure changes; solids and aqueous species are not counted.For the equilibrium:$$A_{(s)} + 2B_{(g)} \rightleftharpoons 2C_{(aq)} + D_{(g)}$$Gaseous moles on the forward side = $2$ from $2B_{(g)}$.Gaseous moles on the backward side = $1$ from $D_{(g)}$.When pressure is decreased, the equilibrium shifts toward the side with more gas particles.So the equilibrium shifts to the left, favouring the backward reaction.This means the rate of the backward reaction will increase.Answer:C. rate of backward reaction will increase