Why are acid base neutralization reactions exothermic?
exothermic nature of the reaction is due to the enthalpy change of the reaction. No matter what acid or base is used, the basic reaction which brings about the enthalpy change is that between H+ ions and OH- ions. If the acid is a strong one, it will dissociate in the medium to yield higher number of H+ ions, thus, if the base is also strong, reaction between H+ and OH- will go on to bring about a higher change in the temperature. Weak acids ( such as acetic acid and many organic acids) dissociate partially and thus, they cannot release much number of H+ ions as a strong acid would do. Same is true for base too.
