Avogadroâ€™s law states that equal volumes of all gases at the same temperature and pressure contain the same number of molecules.

Avogadroâ€™s law in the mathematical form is as follows:

V/n = k

Here, V is the volume of the gas, n is the amount of substance in the gas and k is the proportionality constant.

Avogadroâ€™s law is named after Amedeo Avogadro (1776 to 1856), an Italian scientist, along with the Avogadroâ€™s number or constant 6.022 x 10^{23}.Â This was due to his notable contributions to molecular theory and for his formulation of the Avogadroâ€™s law.

Two practical examples of the Avogadroâ€™s law are as follows:

1)Â Â Â Â Â Blowing and inflating a balloon:Â The balloon increases in volume with the increase in the number of molecules of air inside the balloon and thus exemplifies Avogadroâ€™s law in a simple manner.

2)Â Â Â Â Â Rapid release of projectiles like bullets:Â The sudden rapid release of a bullet as it is pushed out of its trigger during a shooting sports event shows Avogadroâ€™s law in action. Â The reaction of gunpowder behind a bullet as the trigger is released increases the gas particles behind the bullet with an increase in volume which quickly projects the bullet forward out of the gun.

You may have heard of Avogadroâ€™s number which is 6.022 x 10^{23}.Â The Avogadroâ€™s number 6.022 x 10^{23} is the number of molecules found in 1 gram-mole of a gas known as its molecular weight.Â The volume occupied by 1 gram mole of a gas is the same for all gases and is around 22.4 liters at a standard temperature and pressure.Â For example, the molecular weight of carbon dioxide is 44 and 1 gram mole of carbon dioxide will contain 6.022 x 10^{23} molecules.Â The molecular weight of oxygen is 32. Â How many molecules will 1 gram mole of oxygen contain?Â Yes, 1 gram mole of oxygen occupying the same volume as 1 gram mole of carbon dioxide will contain the same number of molecules, that is, 6.022 x 10^{23 }as per Avogadroâ€™s law.Â Â One of the foundation stones of studying modern chemistry and doing stoichiometry calculations is the use of the Avogadro number.

photo credit: pillowhead designs via photopin cc