Avogadro's law is a gas law named after Amedeo Avogadro who, in 1811, hypothesized that two given samples of an ideal gas, at the same temperature, pressure and volume, contain the same number of molecules.

Mathematical definition

Avogadro's law is stated mathematically as:

Where: V is the volume of the gas. n is the amount of substance of the gas. k is a proportionality constant.

The most significant consequence of Avogadro's law is that the ideal gas constant has the same value for all gases. This means that:

Where: p is the pressure of the gas. T is the temperature in kelvin of the gas

Ideal gas law

A common rearrangement of this equation is by letting R be the proportionality constant, and rearranging as follows:

pV = nRT

This equation is known as the ideal gas law.

Molar volume

Taking STP to be 101.325 kPa and 293.15 K, we can find the volume of one mole of a gas:

For 100.000 kPa and 273.15 K, the molar volume of an ideal gas is 22.414 dm3mol-1.