The adsorption of a gas into a solid surface is mainly of two types :
(a) Physical Adsorption
This is due to the gas molecules being held to the solid surface by van der Waal’s attractive
forces. It is also referred to as van der Waal’s Adsorption. For example, adsorption of hydrogen or
oxygen on charcoal is Physical Adsorption.
(b) Chemical Adsorption or Chemisorption
In this kind of adsorption, the gas molecules or atoms are held to the solid surface by chemical
bonds. These bonds may be covalent or ionic in nature. For example, hydrogen is chemisorbed
on nickel. Hydrogen molecules is first adsorbed by van der Waal’s forces and then dissociates. The
hydrogen atoms are thus chemisorbed on nickel.

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