CBSE Class 12-science Answered

Factors Affecting Adsorption of Gases by Solids 

A] Nature and surface area of adsorbent:

1. The same gas is adsorbed to different extents by different solids at the same temperature.

2. Also, greater the surface area of the adsorbent, greater is the volume of the gas adsorbed.

    So, substances such as charcoal and silica gel are the best adsorbents because they have high surface area and a highly porous structure.

3. Thus, finely divided substances provide a larger adsorption power than when they are present in the compact form

 B] Nature of gas being adsorbed:

1. Different gases are adsorbed to different extents by the same adsorbent at the same temperature.

2. The critical temperature of a gas is the minimum temperature above which the gas cannot be liquefied however high the pressure may be.

3. It is practically observed that higher the critical temperature of a gas, greater is the amount of gas adsorbed,

    i.e. the gas which is more easily liquefiable or is more soluble in water is more readily adsorbed.

C] Temperature:

1. It is observed that the adsorption decreases with an increase in temperature.

   For example, one gram of charcoal adsorbs about 10 ml of N₂at 273 K, 20 ml at 244 K and 45 ml at 195 K. 

D] Pressure:

1. At constant temperature, the adsorption of gas increases with an increase in pressure.

2. At low temperature, the adsorption of gas increases very rapidly as the pressure is increased.

E] Activation of the solid adsorbent:

1. Activation of an adsorbent is increasing the power of the adsorbent.