Enthalpy of Neutralisation
The enthalpy change when an acid and a base react to form one mole of water under standard conditions.
Formula / equation
H⁺ + OH⁻ → H₂O, ΔH = −57.1 kJ
Unit
kJ/mol
In depth
For any strong acid with any strong base the value is essentially constant, because the only reaction actually occurring is the combination of hydrogen and hydroxide ions. Weak acids or bases give smaller magnitudes, since energy is consumed in completing their ionisation.
Examples in the real world
HCl with NaOH gives −57.1 kJ/mol; ethanoic acid with NaOH gives only about −55.2 kJ/mol.