# Hydrocarbon

A compound made only of hydrogen and carbon atoms. Most fuels are hydrocarbons.

Chemistry (school) · Part 08: Carbon chemistry and the Earth · Card 2 of 10 · Last updated 2026-10-19

## Analogy

Hydrocarbons are chains built from only two kinds of bead, hydrogen and carbon.

## Example

**Hydrocarbon formulae**

Methane: CH4
Ethane: C2H6
Propane: C3H8

## In practice

Methane, propane and octane are hydrocarbons.

## Practice

### Flashcards

- **What is a hydrocarbon?** A compound containing only hydrogen and carbon.

### Interview questions

**Describe how fractional distillation separates crude oil and explain why the fractions come out at different heights.**

- Oil is heated and vapours enter the column
- The column is hotter at the bottom and cooler at the top
- Molecules condense where the temperature is below their boiling point
- Smaller molecules with low boiling points rise higher

## Questions people ask

### Why do hydrocarbons burn so well?

They release a lot of energy when carbon and hydrogen combine with oxygen to form carbon dioxide and water. The bonds in the products are much stronger than those in the fuel, so the reaction is strongly exothermic. This is why they work well as fuels.

### Why do bigger hydrocarbons burn less easily?

Long-chain hydrocarbons are thicker, less runny and have higher boiling points, so they are harder to vaporise and mix with oxygen. They do not ignite as easily and burn with a smoky flame. Short-chain ones like petrol are runny, vaporise easily and burn cleanly.

## Related concepts

- [Crude oil](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-8/chemistry-school-part-8-concept-1)
- [Fractional distillation](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-8/chemistry-school-part-8-concept-3)
- [Alkane](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-8/chemistry-school-part-8-concept-4)
- [Alkene](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-8/chemistry-school-part-8-concept-5)

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