What is combustion?

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Key points

  • Combustion is another name for burning.
  • In a combustion reaction, fuel is burned and reacts with oxygen to release energy.

What do petrol, natural gas, wood and coal have in common?

They are all fuels, which means that they can be burned to release energy.


Watch the video below to find out what happens during a reaction.

While you are watching, think about the meanings of combustion, fuel and oxidation.

What is a combustion reaction?

What are the three parts of the fire triangle?

A fuel, oxygen and heat are needed for a fire. If one of these is removed, a fire will go out.

What is a combustion reaction?

Combustion is another word for burning. In a combustion reaction, a is heated and it reacts with oxygen.

The fire triangle summarises the three things needed for combustion - a fuel, heat and oxygen. If one of these things is removed from a fire, the fire goes out.

When fuels burn in combustion reactions, they release useful thermal energy (heat). Combustion reactions are used to heat our homes, power most cars, and to generate a lot of our electricity.

A fire needs a fuel, oxygen, and heat

What is the difference between combustion and burning?

Nothing! They mean the same thing. Combustion is the scientific word for burning.

Oxidation reactions

An reaction is one where a substance reacts with oxygen and produces oxides. An oxide is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. Combustion is an example of an oxidation reaction.

Many fuels contain carbon and hydrogen atoms. These fuels burn to produce oxides, carbon dioxide and water. Water, HO, is dihydrogen monoxide. Carbon dioxide, CO, is a that causes .

Power station's emit carbon dioxide

Water could also have the chemical name dihydrogen oxide or dihydrogen monoxide because two hydrogen atoms are bonded to one oxygen atom.

Petrol is a fuel which is used in cars. Petrol is made from molecules which contain only carbon and hydrogen atoms. What is produced when petrol burns in a car engine?

Carbon dioxide (CO) and water (HO) which are both oxides.

Working scientifically

Working safely with combustion in the lab

Combustion reactions can be investigated in a science lab.

If you are working with combustion it is important to work safely.

To work safely, you need to identify hazards eliminate them, or if this isn't possible, control the risk.

What safety precautions would you take to protect yourself when investigating combustion reactions?

  • Wearing safety goggles
  • Wearing protective gloves
  • Wearing a protective lab coat.
  • Tying back hair and tucking away loose clothing, such as ties.

These precautions will help reduce the risk of injury from the combustion investigation like getting burnt.

Find out more about how to work safely in science.

Combustion equations

Combustion reactions can be described using word and symbol equations.

The fuel used in gas barbeques is butane. Butane molecules contain only carbon atoms and hydrogen atoms and it is written as CH.

When the butane burns, the carbon atoms react with oxygen in the air and carbon dioxide, and the hydrogen atoms react with oxygen to make water.

The word equation for the combustion of butane is, butane + oxygen → carbon dioxide + water.

The symbol equation for the combustion of butane is, CH + O → CO + HO

Like all combustion reactions, oxygen will always be one of the and be on the left of the equation. Most combustion reactions produce carbon dioxide and water, so these chemicals are written as the on the right of the equation.

Gas barbeque using fuel to cook

Charcoal is a fuel that contains carbon atoms but no hydrogen atoms. What is the word equation for the combustion reaction which occurs in a charcoal barbeque?

Carbon + oxygen → carbon dioxide


Watch this video to see how a combustion reaction can be represented with a word and symbol equation.

CH is the formula for methane, the largest component of the natural gas used by the oven.

This chef uses combustion daily when working with their oven

In the video, methane reacts with oxygen in a combustion reaction. What is the product?

The product of the reaction is carbon dioxide (CO) and water (HO).

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