Many power plants produce energy by burning carbon-based fuels, which also produces carbon dioxide. Carbon dioxide is a greenhouse gas, so over-production can have negative effects on the environment. Use enthalpy of formation data to calculate the number of moles of CO_2(g) produced per megajoule of heat released from the combustion of each fuel under standard conditions (1 atm and 25 degree C). coal, C(s, graphite); natural gas, CH4(g); propane, C_3H_8(g); octane, C_8H_18(i) (delta Hf^degree = -250.1 kJ middot mol^-1).