WAEC Chemistry 2017 Paper

Concept:A catalyst changes the rate of a reaction by lowering the activation energy.Explanation:The activation energy is the minimum energy needed for reactants to form products.A catalyst provides an alternative pathway with a lower activation energy.This means more reactant particles have enough energy to react, so the reaction speeds up.A catalyst does not change the free energy ($\Delta G$) of the reaction.It also does not change the enthalpy change ($\Delta H$) or the equilibrium position.Therefore, the property affected by a catalyst is the activation energy.Answer:A. activation energy