[bloak]

Coal: C + O2 -> CO2

Gas: CH4 + 2O2 -> CO2 + 2H2O

I don't know off hand exactly how many joules of energy (heat) are produced per mole in each case but it's not surprising that gas gives more joules per mole of CO2: it's a bit like you're burning hydrogen at the same time.

EDIT: It's relevant that O-H bonds are stronger than C-H bonds, presumably.

[988747]

You also need to consider that H2O itself is also a greenhouse gas, much worse than CO2, although much easier to remove from atmosphere.

[nix23]

>H2O

Water...

[adolph]

Thanks, that makes some sense. I wonder how that additional bond works in the hydrolox to methalox comparison of rocket fuels.

[pfdietz]

Coal is more like CH on average.