Page 29 - 11-chem-3

3.GASES eLearn.Punjab

Following are the fundamental postulates of this kinetic theory of gases.
1. Every gas consists of a large number of very small particles called molecules. Gases like He, Ne,

Ar have monoatomic molecules.
2. The molecules of a gas move haphazardly, colliding among themselves and with the walls of the

container and change their directions.
3. The pressure exerted by a gas is due to the collisions of its molecules with the walls of a container.

The collisions among the molecules are perfectly elastic.
4. The molecules of a gas are widely separated from one another and there are sufficient empty

spaces among them.
5. The molecules of a gas have no forces of attraction for each other.
6. The actual volume of molecules of a gas is negligible as compared to the volume of the gas.
7. The motion imparted to the molecules by gravity is negligible as compared to the effect of the

continued collisions between them.
8. The average kinetic energy of the gas molecules varies directly as the absolute temperature of

the gas.
Keeping inviewthebasic assumptions given above,R.JClausiusdeducedanexpressionforthepressure
of an ideal gas. Actually,pressure on the walls of the vessel is due to collisions. Whenever the molecules
move they collide among themselves and with the walls of the container. Due to these collisions,a
force is exerted on the walls of the container. This force when divided by the area of the vessel gives
force per unit area, which is called pressure. In this way, the final form of kinetic equation is as follows.

PV = 1 − . . . . . . . . . (13)

3 mNc2

Where,

P = pressure
V = volume
m = mass of one molecule of the gas
N = number of molecules of gas in the vessel
c2 = mean square velocity

29