Heat released when an acid and base form one mole of water, about -57 kJ for strong ones.
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The enthalpy of neutralization is the heat change when an acid and a base react to form one mole of water. For a strong acid and a strong base the net reaction is H+ plus OH- forming H2O, and the value is close to -57.3 kJ per mole of water formed. Strong electrolytes are fully dissociated, so the only net chemical change is the formation of water, and the enthalpy is nearly the same regardless of which salt forms. Weak acids or weak bases give smaller magnitudes, because part of the heat is consumed in ionizing the weak species before neutralization can occur. This value is measured conveniently in a coffee-cup calorimeter.
Key ideas: Strong acid with strong base releases about 57 kJ per mole of water because the net reaction is H+ plus OH- giving water. For a weak acid or base, the observed value is less negative since some energy goes into ionizing the weak species. Use the moles of water formed, which equals the moles of the limiting reagent.
Common mistakes and connections: Students expect different strong acids to give different values, but they are nearly identical. Another error is dividing by total moles of acid and base rather than moles of water formed. Sulfuric acid, which has two protons, requires care with the stoichiometry. It ties to calorimetry and to acid strength.
Strong acid and strong base neutralize at pH 7, releasing about -57 kJ per mole of water formed because the net reaction is always H+ + OH- giving H2O. The interactive lesson shows this as a live animation or chart.
Hydrochloric acid reacting with sodium hydroxide releases about 57 kJ per mole of water, while ethanoic acid gives a smaller release.
Heat released when an acid and base form one mole of water, about -57 kJ for strong ones.
Enthalpy of Neutralization is a intermediate topic in Thermodynamics & Energetics. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Thermodynamics & Energetics first: Standard Enthalpy of Formation, Standard State, Enthalpy of Combustion.
The next topics in Thermodynamics & Energetics are Enthalpy of Solution and Hess's Law.
Yes. The interactive lesson includes a self-check question on Enthalpy of Neutralization, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Enthalpy of Neutralization is topic 22 of 91 in Thermodynamics & Energetics.