Question

Heat of neutralisation of weak acid-strong base is not constant.

• A. True
• B. False

Answer 1

The correct option is A True

The given statement is true.

Heat of neutralisation of weak acid-strong base is not constant. This is because a part of the evolved heat is used to ionise the weak acid.
For example, when HCl (strong acid) reacts with NaOH (strong base), the heat of neutralisation is $-$ 13.7 kcal/mol. But when HCN (weak acid) reacts with NaOH (strong base), the heat of neutralisation is $-$ 2.9 kcal/mol. 10.8 kcal/mol heat is absorbed for the ionisation of HCN.