WAEC Chemistry 2016 Paper

Concept:The rate of a chemical reaction depends on factors that increase the frequency or effectiveness of collisions between reacting particles.Explanation:The given reaction is:$$2\mathrm{HCl(aq)} + \mathrm{CaCO_3(s)} \rightarrow \mathrm{CaCl_2(aq)} + \mathrm{H_2O(l)} + \mathrm{CO_2(g)}$$Here, the reactants are an aqueous acid and a solid carbonate. There is no gaseous reactant in the mixture.I. Pressure: Pressure affects reactions only when at least one reactant is a gas. Since both reactants are in aqueous and solid states, a change in pressure will not affect the rate of this reaction.II. Concentration: Increasing the concentration of $\mathrm{HCl}$ brings more acid particles into contact with $\mathrm{CaCO_3}$, so the rate increases.III. Nature of reactants: Different substances react at different rates. The identity and bonding of $\mathrm{HCl}$ and $\mathrm{CaCO_3}$ inherently determine how fast they react.IV. Temperature: Raising the temperature increases particle kinetic energy, leading to more frequent and more energetic collisions, which speeds up the reaction.Therefore, concentration, nature of reactants, and temperature affect the rate, but pressure does not.Answer:B. II, III and IV only