To calculate the heat of formation of methane CH4 , we need to consider the bond energies of the reactants and products involved in the formation of methane. The formation of methane can be represented by the following reaction:C graphite + 2 H2 g CH4 g First, we need to break the bonds in the reactants. The bond energies required to break the bonds are:1 C=C bond in graphite: 838 kJ/mol2 H-H bonds in H2: 2 436 kJ/mol = 872 kJ/molTotal energy required to break bonds in reactants: 838 + 872 = 1710 kJ/molNext, we need to form the bonds in the product, CH4. The bond energies released when forming the bonds are:4 C-H bonds in CH4: 4 413 kJ/mol = 1652 kJ/molNow, we can calculate the heat of formation of methane Hf using the following equation:Hf = Energy required to break bonds in reactants - Energy released when forming bonds in productsHf = 1710 kJ/mol - 1652 kJ/mol = 58 kJ/molSo, the heat of formation of methane CH4 is 58 kJ/mol.