A combustion reaction is an exothermic chemical reaction between substances , usually including oxygen gas and accompanied by the generation of heat, energy, and light (flame). What is a Combustion Reaction? A combustion reaction is a reaction of a substance with oxygen gas to release relatively large amounts of energy . Because combustion reactions are often characterized by the presence of flames, a substance undergoing combustion is often said to be burning. Combustion, or burning, [1] 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, a chemical reaction between substances , usually including oxygen and usually accompanied by the generation of heat and light in the form of flame.