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 reaction. The formation reaction of methane can be represented as:C graphite + 2 H2 g CH4 g In this reaction, we are breaking two C-H bonds in H2 and forming four C-H bonds in CH4. We don't need to consider the C-C bond energy since there is no C-C bond involved in this reaction.The bond energy values given are:C-H bond energy = 413 kJ/molTo calculate the heat of formation Hf , we can use the following equation:Hf = bond energies of bonds broken - bond energies of bonds formed In this case, we have:Hf = [2 C-H bond energy in H2 ] - [4 C-H bond energy in CH4 ]Hf = [2 413 kJ/mol ] - [4 413 kJ/mol ]Hf = 826 kJ/mol - 1652 kJ/mol Hf = -826 kJ/molThe heat of formation of methane CH4 is -826 kJ/mol.