Vapor
Definition and meaning of Vapor in chemistry.
A vapor is the gaseous form of a substance that is normally a liquid or solid at room temperature and standard pressure. Vapors form when molecules escape from the surface through evaporation (from liquids) or sublimation (from solids).
In more detail
Unlike a gas, which is the natural phase of a substance at standard conditions, a vapor is the gaseous form of a substance that exists as liquid or solid under those conditions. All liquids and solids have a characteristic vapor pressure that increases with temperature, indicating their tendency to enter the vapor phase. The equilibrium between a condensed phase (liquid or solid) and its vapor is fundamental to understanding distillation, evaporative cooling, drying processes, and weather phenomena. Vapors can condense back to their original phase when cooled or compressed.
Key facts
| Field | Physical Chemistry |
|---|---|
| Example substance | Water vapor, H2O |
| Thermodynamic property | Vapor pressure increases with temperature |
| Phase behavior | Reversible by cooling or compression |
Water evaporating from a puddle during a sunny day becomes water vapor, which rises into the atmosphere and can later condense into clouds.
Frequently asked questions
What is the difference between a vapor and a gas?
A gas is the stable phase of a substance at room temperature and pressure, while a vapor is the gaseous form of a liquid or solid under those same conditions.
Does every liquid have a vapor pressure?
Yes, all liquids have vapor pressure at any temperature above absolute zero, though some substances have very low vapor pressures at room temperature.