JAMB Chemistry 2013 Paper

Concept:Apply Le Chatelier’s principle to the forward exothermic reaction with fewer gas moles on the product side.Explanation:The forward reaction is exothermic: $\Delta H = -395.7 \, \mathrm{kJ\,mol^{-1}}$, so heat is treated as a product.Decreasing the temperature shifts the equilibrium to the right to produce more heat, hence more $\mathrm{SO}_{3(g)}$ is formed.Changing pressure or adding a catalyst does not increase the equilibrium yield of $\mathrm{SO}_3$ in this way.Answer:B. decreasing the temperature