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 The standard enthalpy of combustion of methane is given as -890.3 kJ/mol. This value corresponds to the reaction:CH4 g + 2 O2 g CO2 g + 2 H2O l The bond energies for the C-H and C-C bonds are given as 413 kJ/mol and 348 kJ/mol, respectively. However, we do not need the C-C bond energy for this calculation, as there are no C-C bonds involved in the formation of methane.To calculate the heat of formation of methane, we need to consider the bond energies of the reactants and products. The bond energy of the C-H bond in methane is 413 kJ/mol, and there are four C-H bonds in one molecule of methane. Therefore, the total bond energy of the C-H bonds in methane is:4 413 kJ/mol = 1652 kJ/molNow, we need to consider the bond energies of the reactants. The bond energy of the H-H bond in hydrogen gas H2 is approximately 436 kJ/mol. Since there are two moles of hydrogen gas in the reaction, the total bond energy of the H-H bonds in the reactants is:2 436 kJ/mol = 872 kJ/molThe heat of formation of methane can be calculated using the bond energies of the reactants and products:Hf CH4 = Total bond energy of products - Total bond energy of reactants Hf CH4 = 1652 kJ/mol - 872 kJ/mol Hf CH4 = 780 kJ/molTherefore, the heat of formation of methane CH4 is approximately 780 kJ/mol.