determination of the enthalpy change of neutralization(20分)

For strong acids and strong alkalis the molar enthalpy of neutralisation is effectively constant at about -57kJ per mol. This is because strong acids and strong alkalis, and the salts they form, are all completely ionised in dilute solution, so that the reaction is simply the formation of unionised water from H+ and OH- ions.
H+(aq)　+　OH-(aq)　--->　H2O(l)　　delta Hm(298K) = -57 kJ per mol

I hope this can help with your understanding. =)