Distribution of Molecular Speeds

According to Maxwell, in a gas all the molecules are in a state of constant rapid random motion and they collide with one another and with the walls of the vessel. During collision the redistribution of the energy takes place. As a result their speed and the kinetic energy changes.

Therefore, at any instant different molecules have different speed and hence different kinetic energy. At the given temperature even though the speed of the individual molecule continuously changes, the fraction of the molecules having the same speed remains constant and this is known as Maxwell–Bolttzmann Distribution Law.