A combustion reaction is a reaction in which a substance reacts with oxygen gas to release energy in the form of light and heat. So basically it is an exothermic reaction.

Most combustion reactions occur with a hydrocarbon (compounds made up solely of carbon and hydrogen). The products of the combustion of hydrocarbons are carbon dioxide and water.

A figure of combustion reactions

Many hydrocarbons are used as fuel as their combustion releases very large amounts of heat energy.

Examples of combustion reactions

C3H8   + 5 O2    3CO2 + 4H2O + Δ

2C3H8 + 3O    2CO2 + 4H2O + Δ

C3H6O + 4O2    3CO2 + 3H2O + Δ

Combustion is not only important in our everyday lives for the production of energy but also in keeping us alive.  When the cells of our bodies break down sugar (glucose) to release energy they do so by a complete combustion reaction in aerobic cellular respiration.

During aerobic respiration, glucose is combusted in the presence of oxygen to produce carbon dioxide, water, and ATP (energy). A small quantity of heat is also generated in the process since this is an exothermic reaction. The equation for this reaction is:

C6H12O6 + 6O2   →   6CO2 + 6H2O + Energy

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Types of the combustion reactions

There are two types of combustion reactions, based on the extent of completion of a reaction:

Complete combustion

Complete combustion reactions, also known as clean combustion reactions, are the complete oxidation reactions of the fuel. Such reactions often liberate only water and carbon dioxide as the products, apart from heat and light. An example could be the combustion of propane in the presence of oxygen.

C3H8   + 5O2   →   3CO2 + 4H2O

Incomplete combustion

Incomplete combustion reactions are combustion reactions that involve the formation of by-products such as ash and soot. This reaction happens when the supply of oxygen is inadequate, and carbon and carbon monoxide are produced. An example could be the combustion of propane in an environment where oxygen is deficient.

2C3H8 + 9O2   →   4CO2 + 2CO + 8H2O

Complete Combustion Incomplete Combustion
Sufficient amount of oxygen is available The availability of oxygyen is insufficient
Carbon dioxide and water are produced Carbon monoxide and water are produced
The flame is blue in color The flame is yellow or orange in color
Smoke is not produced Smoke is produced
It yields high energy It yields low energy

Environmental impact: global warming due to COproduction

Environmental impact: air pollution due to CO production

Also read: Carbon Monoxide vs. Carbon Dioxide: The Chemistry of CO and CO2

Concepts Berg

What is the definition of a combustion reaction?

A combustion reaction is a chemical reaction in which a substance reacts with oxygen gas, releasing energy in the form of light and heat.

Why is oxygen needed in combustion?

Combustion means that a substance is oxidized producing gaseous products, and oxygen is the best-known oxidizer. Air comprises about 20% of oxygen, at this concentration, oxygen gas will be one of the reactants in almost all combustion reactions.

What is the formula for combustion?

The general equation for a complete combustion reaction is:

Fuel + O2 → CO2 + H2O + Heat

What is an incomplete combustion reaction?

Incomplete combustion takes place when there is not enough oxygen to allow the fuel to react completely and burn in order to produce carbon dioxide and water, instead, the products are carbon monoxide and water.

What is the equation of combustion of gasoline?

Octane combustion equation:

C8H18 + 12.5O2 → 8CO2 + 9H2O + Heat

Is H2 + O2 = 2H2O a combustion reaction?

Yes, it is the equation of combustion of Hwhere it reacts with oxygen to produce water.

Is combustion a fast or slow reaction?

Combustion reactions are very spontaneous as they can be slow or fast depending on the amount of oxygen available.

Is combustion the same as burning?

The combustion that results in a fast flame is called burning.