PHYSICAL ADSORPTION OR PHYSISORPTION OR VAN DER WAALS ADSORPTION
It is the adsorption in which molecules of the adsorbate are held to the surface of the adsorbent by weak Vander Waal’s forces. Thus physical adsorption has tow heat of adsorption of the order of 5 to 10 kcal per mole of the gas. A rise in temperature will increase the kinetic energies of molecules and the molecules will leave the surface thus lowering the extent of adsorption. Another characteristic of physical adsorption is that the adsorption equilibrium is reversible and is established rapidly. Examples; Adsorption of hydrogen or oxygen on charcoal or adsorption of nitrogen on mica.