Gay-Lussac's Law - Pressure-temperature Law

Pressure-temperature Law

Gay-Lussac's name is also associated in physics with another gas law, the so-called pressure law, which states that:

The pressure of a gas of fixed mass and fixed volume is directly proportional to the gas' absolute temperature.

Simply put, if a gas' temperature increases then so does its pressure, if the mass and volume of the gas are held constant. The law has a particularly simple mathematical form if the temperature is measured on an absolute scale, such as in kelvins. The law can then be expressed mathematically as:

or

where:

P is the Pressure of the gas (measured in ATM).

T is the temperature of the gas (measured in Kelvin).

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:

Amontons' Law of Pressure-Temperature: The pressure law described above should actually be attributed to Guillaume Amontons, who, between 1700 and 1702, discovered that the pressure of a fixed mass of gas kept at a constant volume is proportional to the temperature. Amontons discovered this while building an "air thermometer". Calling it Gay-Lussac's law is simply incorrect as Gay-Lussac investigated the relationship between volume and temperature (i.e. Charles' Law), not pressure and temperature.

Charles' Law was also known as the Law of Charles and Gay-Lussac, because Gay-Lussac published it in 1802 using much of Charles's unpublished data from 1787. However, in recent years the term has fallen out of favor, and Gay-Lussac's name is now generally associated with the law of combining volumes. Amontons' Law, Charles' Law, and Boyle's law form the combined gas law. The three gas laws in combination with Avogadro's Law can be generalized by the ideal gas law.