To calculate the standard heat of formation of water H2O , we need to consider the bond energies of the reactants and products. The balanced chemical equation for the formation of water is:H2 g + 1/2 O2 g H2O l Now, let's calculate the energy change for this reaction:1. Breaking the H-H bond in H2 g requires 436 kJ/mol.2. Breaking 1/2 of the O=O bond in O2 g requires 1/2 * 498 kJ/mol = 249 kJ/mol.3. Forming two H-O bonds in H2O l releases 2 * 463 kJ/mol = 926 kJ/mol.The standard heat of formation Hf is the difference between the energy required to break the bonds in the reactants and the energy released when forming the bonds in the products:Hf = Energy required to break bonds - Energy released when forming bonds Hf = 436 + 249 - 926Hf = 685 - 926Hf = -241 kJ/molThe standard heat of formation of water H2O is -241 kJ/mol.