The exact amount of a gas adsorbed at the surface of a solid depends upon the following factors:
(i) Nature of gas (adsorbate):
If critical temperature of gas is higher, the van der Waal’s forces of attraction will be greater so adsorption will be greater. Critical temperatures of a few gases are given below:
| Gas |
H2 |
N2 |
CO |
CH4 |
CO2 |
| Critical Temperature K |
33 |
126 |
134 |
190 |
304 |
(ii) Nature of solid (adsorbent):
Greater the surface area per unit mass of the solid, greater is the extent of adsorption.
(iii) Effect of temperature:
Adsorption is accompained by evolution of heat.
∆H = -ve. According to Le-Chateliers’s principle, the rate of adsorption decreases with increase in temperature.
(iv) Effect of pressure:
At constant temperature, adsorption increases with pressure. If the temperature is kept constant at low value, the effect will be large.
