> In hydrocarbons the majority of energy comes from the oxidation of hydrogen.
That's not quite true.
To add some numbers, the average formula for long-chain hydrocarbons is roughly CH2 (one carbon atom for two hydrogen atoms). The enthalpy of formation of water is -286kJ/mole, and for carbon dioxide it's -394kJ/mole.
Conveniently enough, one mole of long-chain hydrocarbons produces one mole of water and one mole of carbon dioxide.
It's better for pure methane, as with its formula CH4 it produces 2 moles of water for each mole of CO2. So you get 572kJ of energy from hydrogens versus the same 394kJ from carbon.
Formation is just one part of the equation. On the other side there's an additional C-C bond per segment of the hydrocarbon chain longer than methane, which you need to break during combustion.
It's already taken into the account. The CO2 enthalpy of formation has C-C bond breaking "baked in", by convention the "standard" form of an element has zero enthalpy of formation. For carbon, it's graphite with its C-C bonds.
I did neglect the C-H bond enthalpy, but it's close enough to the C-C bond energy to matter too much.
That's not quite true.
To add some numbers, the average formula for long-chain hydrocarbons is roughly CH2 (one carbon atom for two hydrogen atoms). The enthalpy of formation of water is -286kJ/mole, and for carbon dioxide it's -394kJ/mole.
Conveniently enough, one mole of long-chain hydrocarbons produces one mole of water and one mole of carbon dioxide.
It's better for pure methane, as with its formula CH4 it produces 2 moles of water for each mole of CO2. So you get 572kJ of energy from hydrogens versus the same 394kJ from carbon.