# Gay-Lussac's law

Gay-Lussac's law (not to be confused with the Law of Charles and Gay-Lussac) is a gas law that relates the pressure and temperature of an ideal gas at constant volume. It was discovered by Joseph Louis Gay-Lussac in 1802. The law states that the pressure of a fixed amount of gas at fixed volume is directly proportional to its temperature in kelvins. It is expressed mathematically as:

[itex]\frac{P}{T}=k[itex] or [itex]P=kT[itex], where

P is the pressure of the gas (measured in cubic metres in SI units);

T is the temperature of the gas in kelvins;

k is a constant.

This law holds true because temperature is a measure of the average kinetic energy of a substance; as the kinetic energy of a gas increases, its particles collide with the container walls more rapidly, thereby exerting increased pressure.

For comparing the same substance under two different sets of conditions, the law can be written as:

[itex]\frac{P_1}{T_1}=\frac{P_2}{T_2}[itex],

since the ratio P/T is a constant (k).

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