Adsorption is a surface phenomenon in which molecules of a substance (called the adsorbate ) accumulate on the surface of another substance (called the adsorbent ). It occurs due to the presence of unbalanced forces at the surface of solids or liquids, which attract the adsorbate particles. Adsorption can be of two types — physical adsorption (physisorption) , involving weak van der Waals forces, and chemical adsorption (chemisorption) , involving strong chemical bonds. It plays an important role in many processes such as catalysis, purification of gases, and water treatment. Quiz Revision Notes Downloads Quiz Revision Notes Downloads ...