Oxidation << `ok` suh DAY shuhn >> is a chemical reaction in which a substance loses electrons. The term originally referred to any chemical process in which a substance combines with oxygen. This definition of oxidation was formulated by chemists before they discovered that some reactions of this kind could occur without oxygen.
The electrons released during oxidation must be captured by another substance. Thus, oxidation is always accompanied by a reaction called reduction, in which a substance gains electrons. The combined transfer of electrons is often called a redox process. See Reduction.
Oxidation can be demonstrated by heating iron and sulfur together. In this case, each neutral iron atom loses two electrons and becomes an iron ion. The electrons released during oxidation are immediately picked up by sulfur atoms, resulting in the formation of sulfide ions. These sulfide ions combine with the iron ions to form the compound iron sulfide.
The rusting of iron is a common example of the original meaning of oxidation. Iron combines with oxygen in the presence of moisture to form rust. Another example is the formation of such air pollutants as nitrogen oxides and sulfur oxides. Nitrogen oxides are produced when oxygen combines with nitrogen in hot, fuel-burning automobile engines. Sulfur oxides form when oxygen reacts with sulfur in coal-burning furnaces.
Oxidation also occurs inside the human body when food molecules combine with inhaled oxygen to slowly produce carbon dioxide, water, and energy. The combustion of natural gas and other fossil fuels is a form of rapid oxidation.
