The standard enthalpy change for the neutralization reaction of hydrochloric acid HCl and sodium hydroxide NaOH at 25C and 1 atm pressure can be determined using the standard enthalpy of formation values for the reactants and products.The balanced equation for the reaction is: HCl aq + NaOH aq NaCl aq + H2O l Using the standard enthalpy of formation values Hf at 25C:Hf HCl, aq = -167.2 kJ/molHf NaOH, aq = -469.15 kJ/molHf NaCl, aq = -407.27 kJ/molHf H2O, l = -285.83 kJ/molThe standard enthalpy change for the reaction H can be calculated using Hess's law:H = [Hf products ] - [Hf reactants ]H = [ -407.27 kJ/mol + -285.83 kJ/mol ] - [ -167.2 kJ/mol + -469.15 kJ/mol ]H = -693.1 kJ/mol - -636.35 kJ/mol H = -56.75 kJ/molTherefore, the standard enthalpy change for the neutralization reaction of HCl and NaOH at 25C and 1 atm pressure is -56.75 kJ/mol.