The enthalpy of neutralization is the enthalpy change accompanying the reaction of an acid and a base to form a salt and water . For any strong acid and strong base, the enthalpy of neutralization is nearly constant at approximately –13.6 kcal/mol (or –57.1 kJ/mol) because both are almost completely dissociated in aqueous solution . The net chemical change is simply the formation of one mole of water from H+ and OH– ions.

According to the sources, HCl is a strong acid and KOH is a strong base . In contrast, HCN and NH4OH are weak electrolytes . When a weak acid or weak base is neutralized, some energy is consumed for its complete ionization, resulting in an enthalpy change that is less than 13.6 kcal/mol. Therefore, the pair of HCl and KOH will have an enthalpy of neutralization nearly equal to –13.6 kcal/mol.

(Note: The specific numerical value of -13.6 kcal/mol is a standard chemical constant not explicitly stated in the provided snippets, but the classification of these substances as strong/weak electrolytes is supported ).