To calculate the Gibbs free energy change G at standard conditions for the combustion of propane, we first need to find the standard enthalpy change H and the standard entropy change S for the reaction.1. Calculate the standard enthalpy change H for the reaction:H = [ Hf products ] - [ Hf reactants ]H = [3Hf CO2 g + 4Hf H2O l ] - [Hf C3H8 g + 5Hf O2 g ]Since the standard enthalpy of formation for O2 g is zero it's an element in its standard state , we can simplify the equation:H = [3 -393.5 + 4 -285.8 ] - [-103.85]H = -1180.5 - 1143.2 + 103.85H = -2219.85 kJ/mol2. Calculate the standard entropy change S for the reaction:S = [ S products ] - [ S reactants ]S = [3S CO2 g + 4S H2O l ] - [S C3H8 g + 5S O2 g ]The standard entropy for O2 g is 205.0 J/ molK . Now we can plug in the values:S = [3 213.6 + 4 69.9 ] - [269.9 + 5 205.0 ]S = 640.8 + 279.6 - 269.9 + 1025.0 S = 920.4 - 1294.9S = -374.5 J/ molK 3. Calculate the Gibbs free energy change G at standard conditions 298 K :G = H - TSG = -2219.85 kJ/mol - 298 K -0.3745 kJ/ molK Note that we need to convert S to kJ/ molK by dividing by 1000:G = -2219.85 kJ/mol - 298 K -0.0003745 kJ/ molK G = -2219.85 kJ/mol + 111.621 kJ/molG = -2108.229 kJ/molSo, the Gibbs free energy change at standard conditions for the combustion of propane is -2108.229 kJ/mol.