Examples of a chemical change include rusting iron, burning wood, frying an egg and baking a cake. A chemical change occurs when the chemical composition of a substance changes irreversibly.
Chemical changes are divided into three groups: organic changes, inorganic changes and biochemical changes. An example of an inorganic change is oxidation of a metal, such as tarnish or rust. An example of an organic chemical change is the process by which crude oil is turned into gasoline. Biochemical changes refer to changes by living organisms, such as photosynthesis by plants and digestion of food by animals. Chemical changes may result in changes of color, odor, composition and temperature.