<P> Combustion / kəmˈbʌs. tʃ ən / or burning is a high - temperature exothermic redox chemical reaction between a fuel ( the reductant ) and an oxidant , usually atmospheric oxygen , that produces oxidized , often gaseous products , in a mixture termed as smoke . Combustion in a fire produces a flame , and the heat produced can make combustion self - sustaining . Combustion is often a complicated sequence of elementary radical reactions . Solid fuels , such as wood and coal , first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them . Combustion is often hot enough that light in the form of either glowing or a flame is produced . A simple example can be seen in the combustion of hydrogen and oxygen into water vapor , a reaction commonly used to fuel rocket engines . This reaction releases 242 kJ / mol of heat and reduces the enthalpy accordingly ( at constant temperature and pressure ) : </P>
what must be present for a combustion reaction to occur
a fuel ( the reductant ) and an oxidant