The standard enthalpy change for the combustion of methane gas CH4 at 298 K and 1 atm pressure can be determined using the balanced chemical equation for the combustion reaction and the standard enthalpies of formation for the reactants and products.The balanced chemical equation for the combustion of methane is:CH4 g + 2 O2 g CO2 g + 2 H2O l The standard enthalpies of formation Hf at 298 K for the substances involved in the reaction are:Hf [CH4 g ] = -74.8 kJ/molHf [O2 g ] = 0 kJ/mol since it is in its elemental form Hf [CO2 g ] = -393.5 kJ/molHf [H2O l ] = -285.8 kJ/molUsing the formula for calculating the standard enthalpy change of the reaction Hr :Hr = [Hf products ] - [Hf reactants ]Hr = [1 -393.5 + 2 -285.8 ] - [1 -74.8 + 2 0]Hr = -393.5 - 571.6 - -74.8 Hr = -965.1 + 74.8Hr = -890.3 kJ/molTherefore, the standard enthalpy change for the combustion of methane gas CH4 at 298 K and 1 atm pressure is -890.3 kJ/mol.