Chemical Change
When matter undergoes a chemical change, its chemical composition is altered, causing the original substance to be replaced by one or more new substances. Chemical change happens when there is a chemical reaction. Among the reactions that promote chemical change are combustion, electrolysis, oxidation, and tarnishing.
Combustion
Combustion is the chemical reaction that occurs when oxygen gas reacts with a flammable substance to create heat and light. The most common combustion reaction happens between fuel and oxygen. Fuel is any flammable substance that stores energy in the form of heat or light. Examples of fuels are gas, oil, and coal.
The energy of a fuel is released only when the fuel reacts with oxygen. For example, the gasoline used as fuel for cars burns with oxygen and releases energy. The energy that is released powers the engines of vehicles.
