Enthalpy of neutralization
In chemistry and thermodynamics, the enthalpy of neutralization (Template:Math) is the change in enthalpy that occurs when one equivalent of an acid and a base undergo a neutralization reaction to form water and a salt. It is a special case of the enthalpy of reaction. It is defined as the energy released with the formation of 1 mole of water. When a reaction is carried out under standard conditions at the temperature of 298 K (25 degrees Celsius) and 1 atm of pressure and one mole of water is formed, the heat released by the reaction is called the standard enthalpy of neutralization (Template:Math).
The heat (Template:Mvar) released during a reaction is
where Template:Mvar is the mass of the solution, Template:Mvar is the specific heat capacity of the solution, and Template:Math is the temperature change observed during the reaction. From this, the standard enthalpy change (Template:Math) is obtained by division with the amount of substance (in moles) involved.
When a strong acid, HA, reacts with a strong base, BOH, the reaction that occurs is
as the acid and the base are fully dissociated and neither the cation Template:Chem2 nor the anion Template:Chem2 are involved in the neutralization reaction.[1] The enthalpy change for this reaction is -57.62 kJ/mol at 25 °C.
For weak acids or bases, the heat of neutralization is pH-dependent.[1] In the absence of any added mineral acid or alkali, some heat is required for complete dissociation. The total heat evolved during neutralization will be smaller.
- e.g. at 25°C
The heat of ionization for this reaction is equal to (–12 + 57.3) = 45.3 kJ/mol at 25 °C.[2]