The heat of combustion of butane C4H10 can be calculated using the balanced chemical equation for the complete combustion of butane:C4H10 g + 13/2 O2 g 4 CO2 g + 5 H2O l The heat of combustion can be determined using the standard enthalpies of formation Hf for the reactants and products. The standard enthalpies of formation for the substances involved are:Hf C4H10, g = -126 kJ/molHf O2, g = 0 kJ/mol since O2 is in its standard state Hf CO2, g = -393.5 kJ/molHf H2O, l = -285.8 kJ/molUsing these values, we can calculate the heat of combustion Hcomb using the following equation:Hcomb = [4 Hf CO2 + 5 Hf H2O ] - [Hf C4H10 + 13/2 Hf O2 ]Hcomb = [4 -393.5 kJ/mol + 5 -285.8 kJ/mol ] - [-126 kJ/mol + 13/2 0 kJ/mol]Hcomb = -1574 kJ + -1429 kJ - -126 kJ Hcomb = -3003 kJ/molTherefore, the heat of combustion of butane C4H10 gas at 25C and 1 atm pressure, assuming complete combustion, is -3003 kJ/mol.