To calculate the standard enthalpy change for the combustion of 1 mole of methane gas CH under standard conditions, we need to use the standard enthalpies of formation Hf for each substance involved in the reaction. The standard enthalpy of formation is the change in enthalpy when 1 mole of a substance is formed from its constituent elements in their standard states.The balanced chemical equation is:CH g + 2O g CO g + 2HO g The standard enthalpies of formation Hf for each substance are:Hf CH = -74.8 kJ/molHf O = 0 kJ/mol since O is in its standard state Hf CO = -393.5 kJ/molHf HO = -241.8 kJ/molThe standard enthalpy change for the reaction H can be calculated using the following equation:H = [Hf products ] - [Hf reactants ]H = [1 mol -393.5 kJ/mol + 2 mol -241.8 kJ/mol ] - [1 mol -74.8 kJ/mol + 2 mol 0 kJ/mol]H = -393.5 kJ + 2 -241.8 kJ - -74.8 kJ H = -393.5 kJ - 483.6 kJ + 74.8 kJH = -802.3 kJ + 74.8 kJH = -727.5 kJTherefore, the standard enthalpy change for the combustion of 1 mole of methane gas CH under standard conditions is -727.5 kJ.