Question

By giving suitable examples distinguish between the terms absorption and adsorption.

Give the main points of difference between adsorption and absorption.

Answer 1

Sr. No.	Points	Absorption	Adsorption
1.	Definition	Absorption is a process in which one substance penetrates into the bulk (interior) of another substance.	Adsorption is a surface phenomenon where one substance accumulates only on the surface of another substance.
2.	Concentration distribution	In absorption, the concentration of the absorbed substance is uniform throughout the volume of the absorbing material.	Adsorption is when the adsorbed substance’s concentration is higher on the surface than in the bulk.
3.	Phenomenon type	Absorption occurs throughout the bulk of the material and is a bulk phenomenon.	Adsorption is limited to the surface and is therefore a surface phenomenon.
4.	Examples:	Ammonia is absorbed by water, forming ammonium hydroxide; water vapour absorbed by anhydrous calcium chloride; iodine is absorbed by starch; and ink is absorbed by blotting paper.	Ammonia gas is adsorbed on the charcoal surface; bromine is adsorbed by activated charcoal; water vapour adsorbed by silica gel; and oxygen is adsorbed by tungsten.
5.	Energy Changes	Absorption usually involves a volume change and the process may require or release energy.	Adsorption always releases heat (exothermic process) as it involves molecular interaction at the surface.