Question

what is enthalpy of neutralisation and why the enthalpy of neutralization of strong acid and strong bases are constant

Answer 1

Enthalpy of neutralization is the amount of heat produce when an acid reacts with the alkali and produce 1 mole of water.

Heat of neutralization depends upon

Bascity of an acidStrength of an acidStrength of an alkali

In case of strong acid and alkali, complete ionization is possible so 57.3 kj/mol of energy released.

But weak acid or base will not ionise completely in water. Some remains as undissociated molecules in water. Some amount of heat of neutralization is used to ionise undissociated molecules. As some amount of energy consumed, energy release is less in case of weak acid or alkali.