Electrolysis : Heat Of Neutralisation

The heat evolved in the neutralisation of one equivalent of a strong base by one equivalent of a strong acid should be the same for different acids and bases, since the reaction in all cases is the union of hydrogen ions from the acid with hydroxide ions from the base to form practically undissociated water.

This unexpected result is verified by experiment; the heat of neutralisation is, per equivalent of strong acid and base, equal to about 13.7 k. cal.

HCl Aq + NaOH Aq 13.70 HNO₃ Aq +NaOH Aq 13.70

HBr Aq + KOH Aq 13.76 HCl Aq + ½Ba(OH)₂ Aq 13.85.

If the acid or the base is weak the un-ionised acid or base will dissociate as neutralisation proceeds, and this dissociation will in general be attended by absorption or evolution of heat. An example of this behaviour is the neutralisation of hydrofluoric acid. If the salt formed is only slightly ionised (a very rare case), or is insoluble, the heat of neutralisation will also be abnormal, since association of the ions of the salt to form molecules, or precipitation of the salt, is attended by heat changes.

Protein crystallography
Chemistry guide
Electrolysis
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