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

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SUMMARY

The enthalpy of neutralisation for a strong acid and strong base is consistently 13.7 kcal, while that of a weak acid and strong base is lower. This discrepancy arises because the ionization of a weak acid results in fewer H+ ions available for reaction with OH- ions, leading to a reduced formation of water. Consequently, the heat of formation associated with this process is also diminished. The neutralization of a weak acid involves an initial ionization step before the neutralization occurs.

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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?
 
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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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Ionisation of acid takes place first followed by its neutralisation.
 

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