### ideal gas law

(relates pressure, temperature, and volume)

The **ideal gas law** is a simple equation relating pressure, temperature,
and volume of a gas: a gas that follows the equation
is termed an **ideal gas**.
Real gases generally act in this manner through some regime of
temperature and pressure, but fall away from it in others.
It is a simple-but-useful equation of state.

PV = nRT

- P - pressure.
- V - volume.
- T - temperature.
- n - the amount of gas.
- R - gas constant.

R depends upon the unit used for n,
which can be the number of particles, in which case,
R is the Boltzmann constant (k).
Alternately, n can be the number of **moles** (the number of particles
multiplied by **Avogadro's number (N**_{A}),
1.38066 × 10^{23}),
a number used in chemistry to relate numbers of particles to
grams), in which case
R must be analogously adjusted and is known as
the **universal gas constant** (8.3145 joule (J)/mol K).

The *ideal gas law* was developed (indirectly)
from experimental data.
It can now be derived using physics, but assuming some simplifications,
which are approximately true under some regimes.
In effect, it presumes the gas is monatomic
(i.e., not molecules such as H_{2})
and is a better approximation when the gas is hot enough to keep
it that way, which is true of much of the gas in stars,
and the ideal gas law is used in modeling them.
Gases not in such a regime may still approximately adhere to
the ideal gas law to some extent.
Under extreme densities, quantum-mechanical
effects (degeneracy) radically change the behavior.

(*physics,thermodynamics*)
**Further reading:**

http://en.wikipedia.org/wiki/Ideal_gas_law

http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/idegas.html

https://www.khanacademy.org/science/physics/thermodynamics/temp-kinetic-theory-ideal-gas-law/a/what-is-the-ideal-gas-law

**Referenced by pages:**

Brunt-Väisälä frequency

degeneracy

electron degenerate matter (EDM)

electron degeneracy

electron pressure

isothermal core

Lane-Emden equation

number density (n)

phase transition

statistical mechanics

Index