Combustion Reactions
Combustion burns fuel in oxygen to release heat.
About this topic
Combustion is rapid reaction with oxygen that releases heat and light. For hydrocarbons, complete combustion gives carbon dioxide and water: CH4 + 2O2 → CO2 + 2H2O. Incomplete combustion, with limited oxygen, produces carbon monoxide or soot (carbon) as well, and less energy.
Burning needs three things, the fire triangle: fuel, oxygen and a heat source to start the reaction. Removing any of them puts out the fire. The reactions are exothermic because the bonds formed in carbon dioxide and water are stronger than those broken in the fuel. To balance a hydrocarbon equation, balance carbon first, then hydrogen, and oxygen last, doubling if the oxygen count is odd. Combustion of fuels contributes carbon dioxide to the atmosphere.
Worked example: propane, C3H8, burns as C3H8 + 5O2 gives 3CO2 + 4H2O, releasing about 2220 kJ per mole. Yellow flames on a Bunsen burner with the air hole closed indicate incomplete combustion with soot, while blue flames are hotter and cleaner. Carbon monoxide is a colourless, odourless, deadly gas from faulty heaters, so detectors are vital.
Applications: car engines, power stations, heating and cooking, and rocket fuels. Misconceptions are that combustion always involves a flame (rusting and respiration are slow forms) and that burning destroys mass; the products, including gases, have the same total mass as the fuel and oxygen.
Key ideas
- Hydrocarbons produce CO₂ and H₂O
- Incomplete combustion makes CO or soot
- Exothermic
Quick check
Use cases: where Combustion Reactions helps
- Homework: review the key idea behind Combustion Reactions before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Combustion Reactions without notes.
- Visual learning: play with the interactive lab to see how Combustion Reactions changes when you adjust its inputs.
- Teaching a friend: explain Combustion Reactions in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Combustion Reactions?
Combustion burns fuel in oxygen to release heat.
What will I learn in Combustion Reactions?
Hydrocarbons produce CO₂ and H₂O. Incomplete combustion makes CO or soot. Exothermic.
Is Combustion Reactions part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Combustion Reactions lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Combustion Reactions?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.