Surface Chemistry is the branch of chemistry which deals with the phenomenon that occurs on the surfaces or interfaces, such phenomenon includes corrosion. catalysis, crystallisation, etc
Adsorption
Due to unbalanced attraction forces, accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed as adsorption. The molecular species accumulates at the surface is termed as adsorbate and the material on the surface of which the adsorption takes place is called adsorbent, e. g..
( i) O2, H2, C12, NB3 gases are adsorbed on the surface of charcoal.( ii) Silica gels adsorb water molecules from air.
Charcoal, silica gel, metals such as Ni, Cu, Ag, Pt and colloids are some adsorbents.
Important Characteristics of Adsorption
1. It is specific and selective in nature.
2. Adsorption is spontaneous process, therefore change in free energy( ΔG) is negative.
ΔG = ΔH – TΔS,
For the negative value of ΔG, in a system, in which randomness decreases, ΔH must be negative. Hence, adsorption is always exothermic.
Adsorption of hydrogen over Pt is called occlusion.
Desorption
It is a process of removing an adsorbed substance from a surface on which it is adsorbed, is known as desorption.