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# Gas laws

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The gas laws include Boyle's Law, Charles' Law and Graham's Law and describe the relationship between temperature, pressure and volume of gases. They are collectively generalized by the universal gas equation.

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

Boyle's Law, named afer Robert Boyle, states that the volume occupied by a gas at constant temperature is inversely proportional to the pressure applied.

Charles Law, named after Jacques Charles, 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 P and temperature T is given by Charles' Law:

$P = \mathrm{constant} \times T$

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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### Ideal Gas Law

$PV = nRT$

which states that pressure P multiplied by the volume V is equal to the number of moles of the gas n, multiplied by the temperature T and a constant R. In SI units, the pressure is expressed in pascals, the volume in litres, and the temperature in Kelvin.

The ideal gas law incorporates both Charles Law and Boyle's Law.