Gas
Definition and meaning of Gas in chemistry.
Gas is a state of matter in which particles have no fixed shape or volume, moving independently and rapidly enough to spread out and fill any container they occupy.
In more detail
In a gas, intermolecular attractions are weak compared to the kinetic energy of the particles, so molecules travel freely in straight lines between frequent, essentially elastic collisions with each other and the container walls. This behavior is described by kinetic molecular theory and, for many gases under moderate conditions, approximated by the ideal gas law, PV = nRT, which links pressure, volume, temperature, and amount of substance. Because particles are widely spaced, gases are highly compressible and expand to occupy the entire volume available. Real gases deviate from ideal behavior at high pressure or low temperature, where molecular size and attractive forces become significant.
Key facts
| Field | General Chemistry |
|---|---|
| Defining trait | No fixed shape or volume; highly compressible |
| Governing relation | Ideal gas law, PV = nRT |
| Other states of matter | Solid, liquid, plasma |
At room temperature and standard atmospheric pressure, oxygen gas (O2) uniformly fills any container it is placed in and exerts pressure evenly on all its walls.
Frequently asked questions
How is a gas different from a vapor?
A gas is the normal phase of a substance under standard conditions (like oxygen or nitrogen), while a vapor is the gaseous phase of a substance that is a liquid or solid at those same conditions (like water vapor).
Why do gases exert pressure?
Gas pressure results from the countless collisions of rapidly moving gas particles against the walls of their container.