Why is the Enthalpy of Neutralisation Less for a Weak Acid and Strong Base?

[zorro]

The enthalpy of neutralisation of a strong acid and a strong base is fixed (13.7kcal). But the enthalpy of neutralistaion of a weak acid and strong base etc is less than 13.7kcal. Why?

Explanation: Heat of neutralisation is merely the heat of formation of water from H+ and OH- of acid and base resp. For a weak acid, H+ ions will be in lesser quantity. Hence the amount of water formed will be less, consequently its heat of formation will be less. Is this correct?

 

[Borek]

You are on the wrong track, amount of water produced is almost identical in both cases.

What processes take place during neutralization of a weak acid?

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[zorro]

Ionisation of acid takes place first followed by its neutralisation.