Standard enthalpies of formation at 298 K (kJ mol−1) are as follows: CH4(g) = –75, C2H4(g) = +52, CO2(g) = –394, H2O(l) = –286, O2(g) = 0. Each hydrocarbon undergoes complete combustion to CO2(g) and H2O(l).
Identify which fuel—CH4 or C2H4—releases the greater amount of energy per mole upon combustion, and state one brief thermodynamic reason based on the data above.