Factors which affect the extent of adsorption on the solid surface:
The following are the factors which affect the adsorption of gases on the solid surface:
Nature of the adsorbate (gas) and adsorbent (solid):
- Porous and finely powdered solid e.g. charcoal, fullers earth, adsorb more as compared to the hard-non-porous materials. Due to this property powdered charcoal is used in gas masks used in coal mines.
- Gases with high critical temperature are adsorbed at higher extent as compared to gases with lower critical temperatures
The surface area of the solid adsorbent:
The extent of adsorption depends directly upon the surface area of the adsorbent, i.e. larger the surface area of the adsorbent, greater is the extent of adsorption.
Effect of pressure on the adsorbate gas:
- An increase in the pressure of the adsorbate gas increases the extent of adsorption.
- At low temperature, the extent of adsorption increases rapidly with pressure.
- At low pressure, the extent of adsorption is found to be directly proportional to the pressure.
- At high pressure (closer to the saturation vapour pressure of the gas), the adsorption tends to achieve a limiting value.
Effect of temperature:
As adsorption is accompanied by the evolution of heat, so according to the Le-Chatelier’s principle, the magnitude of adsorption should decrease with rising in temperature.
The amount of heat when one mole of the gas is adsorbed on the adsorbent is called the heat of adsorption