Postulates of Kinetic theory of gases
(1) A gas consists of a very large number of molecules. Each one is a perfectly identical elastic sphere.
(2) The molecules of a gas are in a state of continuous and random motion. They move in all directions with all possible velocities.
(3) The size of each molecule is very small as compared to the distance between them. Hence, the volume occupied by the molecule is negligible in comparison to the volume of the gas.
(4) There is no force of attraction or repulsion between the molecules and the walls of the container.
(5) The collisions of the molecules among themselves and with the walls of the container are perfectly elastic. Therefore, momentum and kinetic energy of the molecules are conserved during collisions.
(6) A molecule moves along a straight line between two successive collisions and the average distance travelled between two successive collisions is called the mean free path of the molecules.
(7) The collisions are almost instantaneous (Le) the time of collision of two molecules is negligible as compared to the time interval between two successive collisions.