PlanetPhysics/Ideal Gas Law

The equation that characterizes any amount of a gas is

$pV=nRT$

where $p$ is the pressure, $V$ the volume, $n$ the number of the gas moles and $T$ the absolute temperature of the gas; $R$ the universal gas constant (approximately 8.314472 ${\frac {{\mbox{Pa}}\cdot {\mbox{m}}^{3}}{{\mbox{mol}}\cdot {\mbox{K}}}}$).

The gas law is accurately valid for an ideal gas, but a good approximation for real gases.

The law contains the following gas laws:

• Boyle--Mariotte law ($pV=$\, constant when $n$ and $T$ are constants)
• Gay--Lussac law (${\frac {V}{T}}=$\, constant when $n$ and $p$ are constants)
• Avogadro's law (in equal conditions, equal volumes of different gases contain the same number of molecules)

Alternative definition

The ideal gas law can also be defined using Boltzmann's constant:

$pV=NkT$

The symbols are those defined above, with the difference that $N$ is the number of gas molecules, and $k$ is the Boltzmann constant, $k\approx 1.38\times 10^{-23}{\mbox{JK}}^{-1}$. This form is often preferred by physicists who consider the number of molecules to be more fundamental than the number of moles.