The reaction of oxygen with fuels such as coal, oil and natural gas can also be harnessed to convertthe chemical energy in the fuel into movement energy. This is how we power many ofour machines. The carbohydrates in our food, for example, oxidise to release energy for our bodies. When dead organic material decays, it is actually oxidising. Oxidation also happens to food left exposed to the air and to the cells in our bodies.
Oxygen reacts with most metals.
Sometimes theeffects cannot be seen, such as when an invisible oxide film forms on the surface of a sheetof aluminium. But other metals react more dramatically. Iron, for example, reacts with oxygen in the presence of water to produce the familiar flakes of rust, while potassium instantly catches fire. The formula for oxygen gas is written as O 2 . Most single atoms of oxygen occur high in the atmosphere.