text: in a simple neutralisation experiment, why does the energy change per mole always stay the same? whereas the actual energy change varies? in a simple neutralisation reaction, a strong acid reacts with a strong base to give a simple salt and water.  consider the two half-reactions involved in neutralisation:  a strong acid(ha) dissociates in an aqueous solution to give h+ and a- ions. since it is a strong acid, it dissociates to an extent of 100%  ha(aq) = h+(aq) + a-(aq)  a strong base(boh) dissociates in its aqueous solution to give b+ and oh- ions. since it is a strong base, it dissociates to an extent of 100%  boh(aq) = b+(aq) + oh-(aq)  the a- and b+ ions stay in the aqueous state. on crystallisation, they form the salt ba.  however the reaction mainly involves the combination of h+ and oh- ions to give water.   h+(aq) + oh-(aq) = h2o + 13.7 kcal  thus, neutralisation is actually the combination of h+ and oh- ions to form water irrespective of the acid or base used.  in simple neutralisation, both the acid and base dissociate to 100% to give equal moles of h+ and oh- ions, which combine to form water always releasing 13.7 kcal of heat per mole.  on the other hand, if a weak acid or weak base is involved, some of this heat is used by the weak acid or weak base to undergo dissociation. for example in the reaction between naoh(strong base) and ch3cooh(weak acid), 0.36 kcal is used by each mole of acetic acid to dissociate, thus releasing only 13.34 kcal of heat.