|MadSci Network: Biochemistry|
Combustion is a chemical reaction that is accompanied by the evolution of heat and light. Typically combustion involves the reaction of oxygen with an electron-rich source such as the compounds in wood or natural gas. When combustion occurs, the heat released from the reaction warms the gas around the combustion area. Hot gases may also be relased from the reaction. The warming increases the volume, or space, occupied by these gases (gases expand when heated). What you see as "fire" is light emitted either directly from the combustion source or from the heated gases rising above the combustion source.
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