# Combustion

Burning a substance in oxygen, which gives out energy. A hydrocarbon burns completely to make carbon dioxide and water.

Chemistry (school) · Part 08: Carbon chemistry and the Earth · Card 8 of 10 · Last updated 2026-10-19

## Analogy

Fuel and oxygen combine like two ingredients in an oven, giving heat as the result.

## Example

**Methane burning**

CH4 + 2O2 -> CO2 + 2H2O
Complete combustion
Gives out energy

## In practice

If there is not enough oxygen, carbon monoxide (a poisonous gas) and soot can form instead.

## Practice

### Flashcards

- **What are the products of complete combustion of a hydrocarbon?** Carbon dioxide and water.
- **What gas is made by incomplete combustion and is poisonous?** Carbon monoxide.

### Interview questions

**Explain how burning fossil fuels affects the climate.**

- Burning releases carbon dioxide
- Carbon dioxide traps heat in the atmosphere
- More greenhouse gas means more warming
- This can raise sea levels and change weather

## Questions people ask

### What is the difference between complete and incomplete combustion?

With plenty of oxygen, complete combustion gives carbon dioxide and water. With limited oxygen, incomplete combustion gives carbon monoxide, carbon soot or both, plus water, and less energy is released. A blue flame means complete burning, while a yellow flame suggests incomplete burning.

### Why is carbon monoxide dangerous?

Carbon monoxide binds to haemoglobin in red blood cells, stopping them carrying oxygen around the body. It has no colour or smell, so you cannot tell it is there. Faulty boilers and fires can produce it, so homes should have carbon monoxide alarms.

## Related concepts

- [Greenhouse effect](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-8/chemistry-school-part-8-concept-9)

Web page: https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-8/chemistry-school-part-8-concept-8
Study this card in the app: https://studyvisually.com/app/learn?category=chemistry-school&card=chemistry-school-part-8-concept-8