The reactions below represent neutralization reaction; in which of them is the value of ΔH highest?

A. CH₃CH₂COOH + KOH → CH₃CH₂COOK + H₂O
B. NH₄OH + HCl → NH4 + H₂O
C. NaOH + HCl → NaCl + H₂O
D. CH₃COOH + NaOH → CH₃COONa + H₂O

Correct Answer:

Option C – NaOH + HCl → NaCl + H₂O

Explanation

The enthalpy change of neutralisation involving weak acids are smaller in magnitude compared to that between strong acids and strong bases. This is because weak acids/bases are partially dissociated, which means not all hydrogen ions are free to react with hydroxide ions.

For strong acids and bases, the enthalpy of neutralisation values are always closely similar with the values -57 and -58 KJ/mol. We know that strong acids completely ionize in water. In case of weak acids, only partial dissociation of its ions occurs.