Question.1: Write down the postulates of kinetic theory of gases.

Ans.: Postulates of kinetic theory of gases:

1) Structure of gases: All gases consist of numerous numbers of very small particles. These small particles of gases (atoms or molecules) are solid, spherical and completely elastic.

(ii) Size & shape: Size and shape of a particular gas particle are same but they differ in case of different gases. Particles of different gases are different in size and shape.

(iii) Motion of molecules: The molecules move around restlessly in no particular direction and with a constant velocity. In doing so the molecules collide with each other and sometimes with the wall of the containers. After collision their direction changes.

(iv) Volume (relative): The volume of a particle is negligible with respect to the total volume of the gas.

 (v) Attraction or repulsion: There is no attraction or repulsion between two gas particles or between a particle & the wall.

(vi) Time of collision: The time of a collision is negligible compared to the time between two collisions. The distance (mean) between two collisions is termed as mean free path.

(vii) Pressure: The pressure exerted by the gas is due to the bombardment of its molecules on the walls of the container per unit area.

(viii) Kinetic energy of gas: Kinetic energy of a gas is proportional to its absolute temperature. An increase in temperature causes an increase in the average kinetic energy of gas particles.

(ix) Effect of gravity: There is no effect of gravity on the gas particles.

(x) Pressure of gas: Pressure of gas occurs due to the collisions of particles with the wall. From the above assumptions an equation of motion can be obtained for ideal gases.

The equation is given as, PV =  1/3mNC2

Where, P = Pressure of the gas, V = Volume of gas, N = number of gas molecules, m = mass of each particle, C = root mean square velocity.

This equation is called kinetic theory equation.

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