# Gas laws

The gas laws are a set of laws that describe the relationship between absolute temperature (T), pressure (P) and volume (V) of gases. The laws include Boyle's law, Charles's law, Gay-Lussac's law, Graham's law, Henry's law, and Avogadro's law and they are collectively generalized by the universal gas equation, also known as the ideal gas law.

A gas which obeys gas laws exactly is hypothetical, and is known as an ideal gas (or perfect gas).

Boyle's law, named after Robert Boyle, states that the volume occupied by a gas at constant temperature is inversely proportional to the pressure applied. In other words,

[itex]V = \mathrm{constant} \times \frac{1}{P}[itex]

(or also [itex]P \times V = \mathrm{constant}[itex]).

Gay-Lussac's law, named after Joseph Louis Gay-Lussac, states that the pressure that a gas exerts on the walls of its container is determined by the momentum of the atoms and molecules of the gas, which in turn is determined by the temperature. As the temperature increases the atoms and molecules move faster, and so exert a greater pressure on the walls. If the walls are rigid, such that the volume of the container is held constant, then the relationship between pressure and temperature is given by Gay-Lussac's law:

[itex]P = \mathrm{constant} \times T[itex]

Graham's law, named after Thomas Graham, states that the kinetic energy of two samples of different gases at the same temperature is identical.

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