Adsorption
The accumulation of molecules of a gas or liquid on the surface of a solid.
Unit
mol/g
In depth
Adsorption is a surface phenomenon and must be distinguished from absorption, which involves uptake throughout the bulk. It is always exothermic, since molecules lose translational freedom, and it is the essential first step in every heterogeneous catalytic process.
Examples in the real world
Activated charcoal removing colour and odour from water; silica gel adsorbing moisture in packaging.