The enthalpy of neutralization (ΔHno) is the change in enthalpy that occurs when an acid and base undergo a neutralization reaction to form water and a salt. It is a special case of the enthalpy of reaction.
When a reaction is carried out under standard conditions at the temperature of 297 K and 1 atm of pressure, it is called the standard enthalpy of neutralization.
The heat (Q) released during a reaction is
where m is the mass of the solution, cp is the specific heat capacity of the solution, and ∆T is the temperature change observed during the reaction. From this, the standard enthalpy change (∆H) is obtained by division with the amount of substance (in moles) involved, usually the amount of H+ ions:
The standard enthalpy change of neutralization for a strong acid and base is -57.3 kJ/mol.
The standard enthalpy of neutralization for mineral acids is slightly less exothermic than that of organic acids, because of the partially ionising property of weak acids. The bond between the proton and its conjugate base requires energy to be broken, hence the lower measured value enthalpy change.