The kinetic theory of gases can be defined as a microscopic theory that explains the behaviour of gaseous substances based on the motion of molecules. The postulates of the kinetic theory of gases are:
Gaseous substances feature relatively small molecules that are spaced far apart from each other. Therefore, the majority of the volume occupied by a gaseous substance is empty space.
The molecules of a gaseous substance are constantly in a state of motion and the direction of their motion is random. The number of gaseous molecules moving in a particular direction is approximately equal to the number of gaseous molecules moving in another direction.
The gaseous molecules frequently collide with the walls of their container and also with each other. The pressure exerted by a gas on the walls of its container can be accounted for by these collisions (between the gas molecules and the walls of the container).
The collisions involving the gaseous molecules can be assumed to be perfectly elastic. Thus, there is not any loss in the net kinetic energy due to the collisions. Also, the sum of the kinetic energies of all gaseous molecules in the container is constant (unless an external source disturbs the system).
No attractive or repulsive forces are exerted on any molecule by another (unless a collision occurs).