We talked about fossil fuels and said that the energy we get from them comes from their chemical bonds. The largest source of energy in the U.S. (and the world) is fossil fuels, a lot of that going toward electricity generation.
We get the energy from fossil fuels through combustion, which is the scientific term for burning. Combustion requires two things: a fuel and an oxidant. In our example the fuel is the fossil fuel octane. The oxidant is oxygen, which comes from the air. Our cars have a fuel tank, but if we were on the moon we would need a fuel tank and an oxidant tank. On Earth we’re spoiled because there’s an oxidant everywhere. (Other substances like chlorine and fluorine are also oxidants.)
Octane and oxygen have more energy in their chemical bonds than the products of combustion, which are carbon dioxide and water. That energy has to go somewhere, so it is released as heat. This is an exothermic reaction. In reality, combustion is rarely perfect, so ash and light and other things are formed, too.
This is why we like fossil fuels: you dig them up out of the ground and they have energy in them ready for the taking. That’s so easy! And easy = inexpensive.
