Adsorption is an surface phenomenon in which a substance called as adsorbate gets accumulated on the surface of the solid or liquid which is called as adsorbent rather than in their bulk.It does not gets penetrated through the surface.The atoms in a solid are held by certain binding forces which are mainly Vander Waal’s forces or may be chemical forces.The unbalances or unutilized forces on the surface make it quite active.Now when a solid is broken into two or more pieces,new surfaces gets formed i.e no. of unbalanced forces becomes more.Thus no. of active centres becomes more by taking the adsorbent in a finely divided form.
This finely divided substance or which can be also reffered to as powdered form can be defined as the dry mass of minute separate particles of the substance.Thus when the substance is powdered its surface area gets increased due to increased in no. of its active centres.As adsorption is directly proportional to the surface area,therefore when substance is taken in finely divided or powdered form,adsorption increased and thus it is called that finely divided substance act as more effective adsorbent.For example activated charcoal which is finely divided has a tendency to adsorb many gases like ammonia,phosgene etc.
