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Enthalpy of neutralization

Change in enthalpy during an acid-base reaction From Wikipedia, the free encyclopedia

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In chemistry and thermodynamics, the enthalpy of neutralization (ΔnH) 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 °C) and 1 bar of pressure and one mole of water is formed, the heat released by the reaction is called the standard enthalpy of neutralization (ΔnH).

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.

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 B+ nor the anion A 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. = −12 kJ/mol at 25 °C

The heat of ionization for this reaction is equal to (−12 + 57.3) = 45.3 kJ/mol at 25 °C.[2]

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