To calculate the change in enthalpy H for the combustion of methane CH4 at standard conditions, we need to consider the balanced chemical equation for the combustion reaction:CH4 g + 2 O2 g CO2 g + 2 H2O l Next, we need to know the standard enthalpies of formation Hf for each compound involved in the reaction. The standard enthalpies of formation are as follows:Hf CH4 = -74.8 kJ/molHf O2 = 0 kJ/mol since O2 is in its standard state Hf CO2 = -393.5 kJ/molHf H2O = -285.8 kJ/molNow, we can calculate the change in enthalpy H for the reaction using the following equation:H = [Hf products ] - [Hf reactants ]H = [1 mol -393.5 kJ/mol + 2 mol -285.8 kJ/mol ] - [1 mol -74.8 kJ/mol + 2 mol 0 kJ/mol ]H = -393.5 - 2 285.8 - -74.8 H = -965.1 kJ/molSo, the change in enthalpy H for the combustion reaction of methane CH4 at standard conditions 298 K, 1 atm is -965.1 kJ/mol.