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You could think of energy density as the number of CO2 or H2O molecules produced by combustion per gram of fuel. If a fuel (like gasoline) can produce more H2O

You could think of energy density as the number of CO2 or H2O molecules produced by combustion per gram of fuel. If a fuel (like gasoline) can produce more H2O+CO2 per gram than ethanol, it will have a higher energy density.

baking 6y ago
No. This is explained in the article. That's only true for hydrocarbons which don't contain oxygen atoms. The energy comes from the O2 consumed. Sugar contains oxygen atoms, but those don't contribute to the energy released because burning sugar consumes less O2 per unit mass than burning hydrocarbons. In your example, 9 moles of ethanol produces the same heat as 2 moles of isooctane, but the combustion products are substantially higher: Ethanol: 9C2H5OH+27O2→18CO2+27H2O Isooctane: 2C8H18+27O2→16CO2+18H2O