Kinetic Molecular Theory of Gases

In order to explain the observed behaviour of gases, a model was proposed based on the molecular and kinetic concept of gas molecules. This model takes into account the particulate nature of matter and the constant movement of particles.

Postulates of Kinetic Theory

• All gases are made up of large number of minute particles called molecules.

• Large distances separate the molecules so that the actual volume of the molecules is negligible as compared to the total volume of the gas.

• The molecules are in a state of constant rapid motion in all directions, colliding with one another and also with the walls of the container.

• The molecular collisions are perfectly elastic with no loss of energy and only redistribution of energy during collision.

• There are no attractive or repulsive forces between the molecules.

• The pressure exerted by the gas is due to the bombardment of its molecules on the walls of the container per unit area.

• The average kinetic energy of the gas molecules is directly proportional to the absolute temperature.

On the basis of these postulates an equation for the pressure of the gas is derived as

This is called the Kinetic gas equation where 'N' is the number of molecules in volume 'V', 'm' is the mass of the

    molecule and 'u' is the root mean square velocity of the molecules.