Heat of Neutralization and the Strength of Acids and Alkalis

  1. Heat of neutralization between a strong acid and a strong alkali is always -57.3 kJ mol-1.  Why?
Heat of neutralisation is the sum of of energy absorbed during bond breaking in the acid and alkali and energy released during bond formation of water molecule from H+ ion and OH- ion.  All the reactions form 1 mole of water. 

2.  Heat of neutralization for neutralization involving weak acid or weak alkali is less than -57.3 kJ mol-1.  Why?
Weak acid/akali does not ionises completely in water. Some energy released during formation of water is used to ionises the weak alkali/acid.

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