Vapour and Gas Are Not Quite the Same
Vapour is a substance suspended in air as a gas. Physics distinguishes vapour from true gas by temperature.
Vapour is a substance diffused in the air, especially one that is normally liquid or solid. Physics draws a line that everyday speech ignores: a *vapour* is the gaseous form of something that is liquid at ordinary temperature, so it can be condensed back by pressure alone. A true *gas* is above its critical temperature and no amount of pressure will liquefy it. *The vapours* was a Victorian term for a fainting spell, blamed on fumes rising within the body.
- A gaseous suspension. *Water vapour.*
- Gas — above critical temperature. *A gas.*
- To vaporise. *Vaporise the liquid.*
- The vapours — a fainting fit. *A fit of the vapours.*
- Latin — *vapor*, steam. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun (UK) | vapour | Vapour. |
| Noun (US) | vapor | Vapor. |
| Verb | vaporise | Vaporise. |
| Adjective | vaporous | Vaporous. |
| Latin | vapor | Steam. |
- Water vapour condensed on the glass.Science.
- A gas cannot be liquefied by pressure alone.Distinction.
- She had a fit of the vapours.Historical.
Vapour and gas compared
- Vapour — below its critical temperature, condensable by pressure
- Gas — above its critical temperature, not condensable by pressure alone
- Water vapour is a vapour at room temperature
- Oxygen is a gas at room temperature
- Everyday speech uses the words interchangeably
Latin *vapor*, steam or exhalation, of uncertain further origin.
What is the difference between vapour and gas?
A vapour is below its critical temperature and can be condensed by pressure alone. A true gas is above it and cannot.
What were the vapours?
A Victorian term for fainting or nervous illness, blamed on internal fumes said to rise and affect the brain.