First, we need to write the balanced chemical equation for the reaction between ammonium nitrate and water:NH4NO3 s + H2O l NH4+ aq + NO3- aq + H2O l Now, we can use Hess's Law to determine the enthalpy change for the reaction. Hess's Law states that the enthalpy change for a reaction is equal to the sum of the enthalpy changes for the formation of the products minus the sum of the enthalpy changes for the formation of the reactants.H = [Hf NH4+ + Hf NO3- + Hf H2O ] - [Hf NH4NO3 + Hf H2O ]Substitute the given values:H = [ -132.5 kJ/mol + -206.1 kJ/mol + -285.83 kJ/mol ] - [ -365.4 kJ/mol + -285.83 kJ/mol ]H = [ -132.5 - 206.1 - 285.83 kJ/mol] - [ -365.4 - 285.83 kJ/mol]H = -624.43 kJ/mol - -651.23 kJ/mol H = 26.8 kJ/molThe enthalpy change H for the reaction between ammonium nitrate and water is 26.8 kJ/mol.