Burning fossil fuel

How do a gloopy liquid (oil) [4], a rock (coal) [5], and a gas (natural gas, which is mostly methane) [6], all result in the release of CO2?

Fossil fuels started off as living animals and plants [6]. Organisms that died millions of years ago were buried underground, and after years of being under high pressure and temperature were transformed into a new substance: fossil fuel [9]. Which type of fossil fuel is made depends on the specific conditions during formation [9].

Living organisms are made mostly from carbon and hydrogen [7], so it makes sense that fossil fuels are too [3]! However, they do also contain small amounts of other chemical elements, including oxygen, nitrogen and sulfur [3].

When they are burnt, fossil fuels combine with oxygen from the air [1], creating two new types of molecules: water and carbon dioxide [1].

Fuel and oxygen both consist of atoms (the building blocks of all matter) attached to each other by bonds [8]. When they “react” which each other, the atoms effectively swap bonds, so new combinations of atoms are bonded to each other [8]. The same atoms exist, just in a different arrangement [8].

The carbon atoms from the fuel combine with oxygen atoms from the air to make carbon dioxide [1]. The hydrogen atoms from the fuel combine with oxygen to make water – made up from 2 hydrogen atoms (H) and 1 oxygen atom (O), which is why it is also called H2O[1].

Overall: Fossil fuel + O2 -> CO2 + H2O
The image shows the molecular diagram of this reaction.

Why does this release energy? The energy needed to break the bonds in the fuel is much less than the energy released when new bonds form in CO2 and H2O [1]. The left-over energy is released as thermal energy (heat), which can be used for many things including heating homes and generating electricity [1,2].


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