Enthalpy of Neutralization, ∆Hn

The enthalpy of neutralization (ΔH_n^o) 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 298 K and 1 atm of pressure, it is called the standard enthalpy of neutralization.
The heat (Q) released during a reaction is

Q = m c ΔT

where m is the mass of the solution, c 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:

∆H = - Q/n

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 far greater than that of organic acids, because strong acids ionize completely while organic acids are usually weak and ionize only partially.