Avogadro's law

Avogadro's law states that under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules. This relation a holds exactly for a ideal gases. The law is approximately valid for real gases at sufficiently low pressures and high temperatures.

The specific number of molecules in one mole of a substance is indicated by N_A, a quantity called Avogadro's number. Its value is ≈ 6.022 × 10²³ For example, the molecular weight of oxygen is 32.00, so that one mole of oxygen has a mass of 32.00 grams and contains N_A molecules.

The volume occupied by one mole of an ideal gas is about 22.4 liter (0.791 cubic feet) at 0° C and 1 atmosphere.

The law was first proposed in 1811 by the Italian physicist Amedeo Avogadro, but it was not generally accepted until after 1858, when the Italian chemist, Stanislao Cannizzaro constructed a logical system of chemistry based on it.