To calculate the heat of formation Hf of methane CH4 , we need to consider the bond energies of the reactants and products. In this case, we are given the bond energies for C-C and C-H bonds. However, we also need the bond energies for the C=O and O=O bonds, as they are involved in the formation of methane from its elements carbon and hydrogen . The bond energies for C=O and O=O are approximately 799 kJ/mol and 498 kJ/mol, respectively.The formation of methane can be represented by the following chemical equation:C graphite + 2 H2 g CH4 g Now, we can calculate the Hf using the bond energies:Hf = bond energies of reactants - bond energies of products For the reactants, we have one C=O bond and two O=O bonds: bond energies of reactants = 1 * 799 kJ/mol + 2 * 498 kJ/mol = 1795 kJ/molFor the products, we have four C-H bonds: bond energies of products = 4 * 413 kJ/mol = 1652 kJ/molNow, we can calculate the Hf:Hf = 1795 kJ/mol - 1652 kJ/mol = 143 kJ/molSo, the heat of formation Hf of methane CH4 is approximately 143 kJ/mol.