What Are the Gas Laws?

The gas laws are a set of physico-chemical laws that describe the behavior of gases when they are in a closed system.

What are the gas laws?

These laws were developed in the late 18th century and mathematically relate pressure, temperature, and volume for a given gas.

The equation of state of an ideal gas is derived from the kinetic theory of gases that explains the behavior of the particles of a gas ( atoms and molecules). The moving particles (kinetic energy) collide with each other and with the container walls, influencing pressure, temperature and volume.

The most important gas laws are:

1. Ideal Gas Law

The ideal gas law is one of the gas laws and represents the equation of state of an ideal gas. It is a good approximation of the behavior of some gases under some conditions, although it has some limitations.

The ideal gas law can be expressed with the following equation:

P V = n R T


  • P is the pressure.

  • V is the volume.

  • n is the amount of the substance or number of moles.

  • R is a constant that depends on the gas.

  • T is the temperature.

2. Boyle-mariotte's Law

The Boyle-Mariotte law states that at constant temperature, the volume of a gas is inversely proportional to the increase in pressure.

This law describes the pressure-volume relationship of a gas in an isothermal process, that is, without varying the temperature. From the point of view of modern physics, the law is a consequence of the Clapeyron-Mendeleev equation.

Robert Boyle experimentally established this law in 1662. Edm Mariotte, in turn, rediscovered it on his own in 1676.

3. Gay-lussac Law 

Gay-Lussac's law states that at constant volume, the pressure of a given mass of gas is directly proportional to its absolute temperature. That is, as the temperature increases, the pressure increases if the volume remains constant.

P / T = constant

Gay-Lussac's law is also known as the isochoric transformation law because it is carried out at constant volume. It was discovered by the French physicist Jacques Charles in 1787 but was first enunciated by Louis Joseph Gay-Lussac in 1802.

Jacques Charles demonstrated that when a gas undergoes an isochoric transformation, the relationship between its pressure and temperature remains constant.

The molecular explanation of Charles's law is that by raising the temperature of a quantity of gas, the average velocity of its molecules increases. The molecules hit the walls of the container more frequently and have a stronger impact, thus increasing the pressure exerted by the gas molecules on them.

On this site we will use the name Gay-Lussac's law to refer to the relationship between pressure and temperature at constant volume and Charles's law for the relationship between volume and temperature at constant pressure.

4. Charles Law

Charles's law states that if the pressure and quantity of a gas is unchanged, the relationship between volume and temperature remains constant and they are directly proportional to each other.

V / T = constant

Sometimes the name Gay-Lussac is also used to refer to Charles's law that relates the temperature and pressure of a gas at constant pressure. In reality, Louis Joseph Gay-Lussac announced Charles's law in 1802, while Jacques Charles had discovered it 15 years earlier, in 1787.

In 1702, Guillaume Amontons had already anticipated this relationship in gases.

5. Avogadro's Law 

Avogadro's law states that gases with the same volume, temperature, and pressure contain the same number of particles (or molecules). So the number of molecules in a specific volume of gas is independent of the size or mass of the gas molecules.

The number of molecules in a mole of substance is Avogadro's number: approximately 6.022 · 10 23 particles / mole.

Consequently, the densities of the different gases are, under the same conditions of temperature and pressure, proportional to their molecular masses.

This law is named after Amedeo Avogadro, who raised it in 1811.

6. Other Gas Laws 

  • Graham's Law. This law states that the rate of diffusion of gas molecules is inversely proportional to the square root of their density.

  • Dalton's law (partial pressure law) -

  • Henry's Law.


Published: December 1, 2021
Last review: December 1, 2021