JAMB Chemistry 2022 Paper

Concept:Complete neutralisation of a strong acid with a strong base releases the highest heat of neutralisation.Explanation:The enthalpy of neutralisation, $\Delta H$, is the heat change when one mole of water is formed from acid–base reaction.For a strong acid and a strong base, the reaction is simply:$\mathrm{H^+ + OH^- \rightarrow H_2O}$ with $\Delta H \approx -57.1\ \mathrm{kJ\,mol^{-1}}$.This value is high because both reactants are fully ionised in water.Weak acids and weak bases are only partially ionised.Some energy is used to complete their ionisation, so less heat is released.Therefore, reactions involving weak acids or weak bases have smaller enthalpy changes.Among the options, only $\mathrm{NaOH + HCl \rightarrow NaCl + H_2O}$ is a reaction between a strong base and a strong acid.Options A and D involve weak acids, while option B involves a weak base.Thus, the greatest $\Delta H$ value is recorded for the strong acid–strong base neutralisation.Answer:C. $\mathrm{NaOH + HCl \rightarrow NaCl + H_2O}$