Kinetic Theory of Gases

All the general properties of gases are based upon experimental observation. To explain these theoretically a theory was put forward known as Kinetic Theory of Gases. The theory was first proposed by Bernoulli in 1738 and later extended by Clausius, Maxwell, Boltzman, Vanderwaal & Jeans. The main postulates of this theory are as follows;

• Every gas is made up of a large number of extremely small particles called Molecules. All the molecules of a particular gas are Identical in mass and size.
• The intermolecular distances in gas molecules are very large so that actual volume of molecules is negligible as compared to the total volume of gas.
• There are no attractive forces between the molecules of the gas. They are completely independent of each other.
• The gas molecules are not at rest but moves randomly. During their motion, they collide with one another and also with walls of container.
• The pressure of gas is due to bombardment of gas molecules against the walls of container.
• The collisions of gas molecules with each other and with walls of container are perfectly elastic i.e. total Kinetic energy remains conserved before and after collision, however energy may get redistributed.
• The force of gravitation on the molecules is also supposed to be negligible.
• Since the molecules are moving with different velocities, so they possess different kinetic energy. However, the average Kinetic energy of gas is directly proportional to the absolute temperature of gas.

On the basis of above postulates, following Mathematical expression, commonly known as Kinetic Gas Equation is derived.

PV=⅓ mnu²

Where, P=pressure of gas

V=volume of gas

m=mass of gas molecule

n=no. of gas molecules present in given mass of gas

u=root mean square velocity.