Energy from Carbon-based Fuels
When pure carbon burns, each atom in the carbon combines with the two oxygen atoms in an oxygen molecule, to make a carbon dioxide molecule:
In the above models, carbon atoms are black and oxygen atoms are red. Good quality coal is almost pure carbon. The above reaction is what happens when coal burns. Coal is used mostly to power electrical power plants. Twenty-five percent (one-fourth) of the world's energy comes from coal.
When natural gas (methane) burns, each molecule of methane (CH4) combines with the four atoms in two molecules of oxygen, to make two molecules of water (H2O), and one molecule of carbon dioxide (CO2).
Have you figured out what kind of atom is represented by the yellow balls in the above model? Have you noticed that the total number of hydrogen atoms before the reaction (on the left side of the arrow) is equal to the total number of hydrogen atoms after the reaction (on the right side)? Also, there are four oxygen atoms before and after; and there is one carbon atom before and after. This is an example of a chemical reaction. We say that atoms are CONSERVED in a chemical reaction. Natural gas is used mostly for heating homes, making hot water, and cooking. Twenty-three percent (almost one-fourth) of the world's energy comes from natural gas.
When gasoline burns, two molecules of octane (C8H18) combine with twenty-five oxygen molecules (50 oxygen atoms!) to produce sixteen carbon dioxide (CO2) molecules and eighteen water molecules (H2O). We considered showing all of the molecules involved, but decided that it would be too confusing. As before, all of the atoms are conserved in this chemical reaction:
Nearly all of the world's transportation depends upon reactions similar to this to propel civilization's cars, trucks, aircraft, and ships.
Some of the molecules in auto fuel are a little bit shorter than octane, and the molecules in the diesel used in trucks and the jet fuel used in airplanes are a little bit longer. The molecules in bunker crude used in ships are longer yet. In all three cases, the lengths of the molecules vary, but the atoms involved are the same.
Gasoline, diesel, and bunker crude all come from petroleum or crude oil. Sometimes, we just say "oil" when we mean crude oil, petroleum, or the fuel that comes from it.
To produce energy from carbon-based fuels we ALWAYS burn carbon or carbon-chain molecules, and we ALWAYS produce carbon dioxide. Eighty-six percent (six-sevenths) of the world's energy comes from carbon-based fuels. ALL of the carbon-based fuels produce carbon dioxide when they are burned. Only fourteen percent (one-seventh) of the world's energy comes from sources that are NOT carbon-based. (Which means that 12.9 Terawatts, out of the worlds total rate of 15 Terawatts, comes from carbon-based fuel: six-sevenths of 15 = 12.9.)