To calculate the heat of formation of water, 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 First, let's consider the bond energies of the reactants:1. One H-H bond in H2 molecule: 1 436 kJ/mol = 436 kJ/mol2. Since there is only 1/2 O2 molecule, we don't need to consider the O=O bond energy in this calculation.Now, let's consider the bond energies of the product:1. Two O-H bonds in H2O molecule: 2 463 kJ/mol = 926 kJ/molThe heat of formation Hf can be calculated using the following equation:Hf = bond energies of products - bond energies of reactants Hf = 926 kJ/mol - 436 kJ/mol = 490 kJ/molSo, the heat of formation of water H2O is 490 kJ/mol.