Pressure exerted by a Gas :-

Let us consider one mole of a gas in a cubical container of side = l  gases particles collide with the walls of container & exert pressure. The pressure exerted is defined as the momentum imparted by the gas molecules per unit area per unit time on the walls of the container.

Let us deal with a molecule in X- direction.

Initial momentum before collision = mVx

Momentum after collision = - mVx

Change in momentum per collusion = - mVx – mVx = - 2 mVx  =|2mVx|

Time between two successive collision = 2 l / Vx.

Therefore, momentum transferred to the wall in one sec. by on molecule.

= momentum transferred in one collision x no. of collision in one sec.

Force = momentum transferred to the wall

Pressure exerted by molecule = F/A

The total or the average pressure

ρ=MV