To calculate the standard entropy change S of the combustion reaction of methane gas under standard conditions, we need to know the standard molar entropies S of the reactants and products involved in the reaction. The combustion reaction of methane can be represented as:CH g + 2O g CO g + 2HO g The standard molar entropies S at 298 K for the substances involved are:S CH = 186.3 J/molKS O = 205.2 J/molKS CO = 213.8 J/molKS HO = 188.8 J/molKNow, we can calculate the standard entropy change S using the formula:S = S products - S reactants S = [1 S CO + 2 S HO ] - [1 S CH + 2 S O ]S = [1 213.8 + 2 188.8] - [1 186.3 + 2 205.2]S = 213.8 + 377.6 - 186.3 + 410.4 S = 591.4 - 596.7S = -5.3 J/molKThe standard entropy change of the combustion reaction of methane gas under standard conditions is -5.3 J/molK.