To calculate the enthalpy change for the combustion of methane gas CH4 under standard conditions, we first need to write the balanced chemical equation for the combustion reaction:CH4 g + 2 O2 g CO2 g + 2 H2O l Next, we need to use the enthalpies of formation for the reactants and products involved in the reaction. The enthalpies of formation for CH4 and CO2 are given as -74.81 kJ/mol and -393.51 kJ/mol, respectively. We also need the enthalpy of formation for H2O l , which is -285.83 kJ/mol.Now we can use Hess's Law to calculate the enthalpy change for the reaction:H = [Hf products ] - [Hf reactants ]H = [1 -393.51 kJ/mol + 2 -285.83 kJ/mol ] - [1 -74.81 kJ/mol + 2 0 kJ/mol]H = -393.51 - 571.66 + 74.81 kJ/molH = -890.36 kJ/molThe enthalpy change for the combustion of methane gas CH4 under standard conditions is -890.36 kJ/mol.