To calculate the standard enthalpy change for the formation of water vapor H2O g from its elements, we need to consider the balanced chemical equation for the formation of water vapor:H2 g + 1/2 O2 g H2O g Now, we can use Hess's Law to determine the standard enthalpy change for this reaction. Hess's Law states that the enthalpy change of a reaction is the sum of the enthalpy changes of its individual steps.In this case, the enthalpy change for the formation of water vapor is the difference between the enthalpy of formation of water vapor and the enthalpy of formation of the reactants:H = Hf[H2O g ] - Hf[H2 g ] + 1/2 Hf[O2 g ] Given that the standard enthalpy of formation of hydrogen gas H2 g is -241.8 kJ/mol and the standard enthalpy of formation of oxygen gas O2 g is 0 kJ/mol, we can plug these values into the equation:H = Hf[H2O g ] - -241.8 kJ/mol + 1/2 0 kJ/mol H = Hf[H2O g ] - -241.8 kJ/mol H = Hf[H2O g ] + 241.8 kJ/molSince we want to find the standard enthalpy change for the formation of water vapor Hf[H2O g ] , we can rearrange the equation:Hf[H2O g ] = H - 241.8 kJ/molHowever, the given information does not provide the value for H the enthalpy change for the reaction . Therefore, we cannot calculate the standard enthalpy change for the formation of water vapor H2O g from its elements with the given information.