ChemTalk

Combustion Reactions

Core Concepts

In this tutorial you will learn what exactly a combustion reaction is and why it is important. You will also encounter numerous examples of combustion reactions and be able to replicate them on your own.

Topics Covered in Other Articles

What is a Combustion Reaction?

Combustion reactions, often simplified as “combustion,” are chemical reactions between a substance and gaseous oxygen. These combustion reactions are exothermic, release energy in the form of heat and/or light, and occur rapidly. Often combustion reactions will produce carbon dioxide and water, but that isn’t a technical requirement. For a combustion reaction to initially occur, the reactants must meet the minimum activation energy–this is why fire will be often used to get a reaction started. Combustion reactions will then continue until either one of the reactants is depleted.

Examples of Combustion Reactions

Imagine the wood burning in a fireplace. The wood is fuel which continuously reacts with oxygen in the air in a combustion reaction. The fire produced is energy being released in a long exothermic reaction, while the smoke you see is carbon dioxide. Lastly, the process can end in one of two ways. Either the wood will completely burn up and the fire will stop, or if you were to completely seal off the fireplace, the fire would stop because of a lack in oxygen.

Balancing Combustion Reactions

Combustion is most common between hydrocarbons and oxygen, to produce carbon dioxide and water. Balancing a combustion reaction is actually pretty straightforward!

  1. Balance the C atom in the CO2 with the hydrocarbon on the left
  2. Balance the H atom in the H2O with the hydrocarbon on the left
  3. Use the O atoms in the CO2 and H2O to balance the O2 on the left

Remember that chemical reactions don’t need to have whole numbers. If your oxygen is preceded by a fraction, not to worry!

Methane Combustion: CH4 + 2O2 → CO2 + 2H2O

Ethane Combustion: C2H6 + 3.5O2 → 2CO2 + 3H2O

Propane Combustion: C3H8 + 5O2 → 3CO2 + 4H2O

Butane Combustion: C4H10 + 6.5O2 → 4CO2 + 5H2O

Further Reading

Take a deeper dive into the other types of chemical reactions!