Combustion reactions or burning is a complicated sequence of extothermic chemical reactions between a fuel source, and an oxidant that is accompanied by producing heat, or heat and light. The fuel that is responsible for combustion reactions is usually a hydrocarbon. The light can make it self present in the form of a glow or in the form of flames. Direct combustion by oxygen is a reaction regulated by radical intermediates. These conditions for the radical production naturally produce themselves by thermal runways. The heat is generated by combustion is a necessity to keep the high temperature that is required for radical production. In a complete combustion reaction, the substance reacts with the oxidizing element, like oxygen or fluorine. The compounds of each element then react with the fuel in the oxidizing element.

Rapid combustion reactions are a form of combustion where by large quantities of heat and light energy are released. This can most often result in fire. This is more well known in the automotive and machinery industry. These are called internal combustion engines and in thermobaric weapons. When large amounts of gas or fuel are contained in a combustion reaction, it can cause enormous pressure to build up. When it is eventually be released, it not only provides for a large amount noise, but also a large amount of energy if the form or fire and light can be noticed. This type of combustion reaction is known as an explosion. These types do have to involve the presence of oxygen. Oxygenless hydrogen can produce burns as well as chlorine that is combined with hydrogen to create hydrogen chloride. These types release their built up energy in the form of heat and light.

Slower forms of combustion reactions is where the combustion will take place at a lower temperature. Cellular respiration is an example of this type. In complete combustion, the reactant will burn in oxygen, producing a limited number of products. When a hydrocarbon burns in oxygen, the reaction will only yield carbon dioxide and water. When a hydrocarbon or any fuel burns in air, the combustion products will also include nitrogen. When elements such as carbon, nitrogen, sulfur, and iron are burned, they will yield the most common oxides. Carbon will yield carbon dioxide.

An incomplete combustion reaction takes place when there is not enough oxygen to allow for the fuel to react totally with the oxygen that would produce carbon dioxide and water. This combustion is released by the addition of a flame or a solid surface. The resulting chemicals when hydrocarbon burns in the air is called carbon dioxide, water, carbon monoxide, pure carbon and various other compounds like nitrogen oxides.


In combustion reactions, the combustion in oxygen is a radical chain reaction that has many unique, radical intermediates can be participating.  The high amount of energy that is needed for the ignition is described by the unusual structure that is the dioxygen molecule. At its lowest temperature configuration the diooxygen molecule is stable.