To calculate the standard enthalpy change for the precipitation reaction between aqueous solutions of silver nitrate AgNO3 and sodium chloride NaCl to form solid silver chloride AgCl and aqueous sodium nitrate NaNO3 , we need to use Hess's Law. Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step in the reaction, and it is independent of the path taken. First, we need to write the balanced chemical equation for the reaction:AgNO3 aq + NaCl aq AgCl s + NaNO3 aq Next, we need to find the standard enthalpies of formation Hf for each compound involved in the reaction. These values can be found in a standard thermodynamic table. The values are:Hf AgNO3 aq = -124.4 kJ/molHf NaCl aq = -407.3 kJ/molHf AgCl s = -127.0 kJ/molHf NaNO3 aq = -365.6 kJ/molNow, we can use Hess's Law to calculate the standard enthalpy change for the reaction:H reaction = [Hf products - Hf reactants ]H reaction = [ Hf AgCl s + Hf NaNO3 aq - Hf AgNO3 aq + Hf NaCl aq ]H reaction = [ -127.0 kJ/mol + -365.6 kJ/mol - -124.4 kJ/mol + -407.3 kJ/mol ]H reaction = [ -492.6 kJ/mol - -531.7 kJ/mol ]H reaction = 39.1 kJ/molThe standard enthalpy change for the precipitation reaction between aqueous solutions of silver nitrate AgNO3 and sodium chloride NaCl to form solid silver chloride AgCl and aqueous sodium nitrate NaNO3 is 39.1 kJ/mol.