The reaction between hydrochloric acid HCl and sodium hydroxide NaOH to form aqueous sodium chloride NaCl and water H2O is an example of an acid-base neutralization reaction. The balanced chemical equation for this reaction is:HCl aq + NaOH aq NaCl aq + H2O l The standard enthalpy change for this reaction, also known as the enthalpy of neutralization, is approximately -57.3 kJ/mol. This value is negative because the reaction is exothermic, meaning it releases heat to the surroundings.