Doc: Liquefaction of Gases | Chemistry for JEE Main & Advanced PDF Download

7. Critical phenomenon & Liquefaction of gases:

The phenomena of converting a gas into liquid is known as liquefaction. The liquefaction of gas is achieved by controlling P and T as follows:

1. Increasing pressure: An increase in pressure results in an increase in attraction among molecules.

2. Decreasing temperature: A decrease in temperature results in decrease in kinetic energy of molecules.

Critical temperature (T_c) : It is defined as the characteristic temperature for a given gas below which a continuous increase in pressure will bring liquefaction of gas and above which no liquefaction is noticed although pressure may be increased e.g. T_c for CO₂ is 31.2°C.

T_C = 

Critical pressure (P_c) : It is defined as the minimum pressure applied on 1 mole of gas placed at critical temperature, to just liquefy the gas

P_C =

Critical Volume (V_c) : The volume occupied by 1 mole of gas placed at critical conditions.

V_C = 3b (i.e. P = P_c and T = T_c)

8. Collision parameters 

- Mean free path

 =  ( = coefficient of viscosity)

 =

k = Boltzman constant ;  = collision diameter.

- Collision frequency (z) : no. of collision taking place per second per unit volume.

- Collision diameter : Closest distance between the centre of two molecule which are participating in collision.

-  Relative Humidity (RH) : 

At a given temperature

RH =

-  Loschmidth Number 

The number of molecules present in 1 cc of gas (or) vapour at STP.

value : 2.617 × 10¹⁹ 1 cc