Characteristics of Adsorption
(i) Adsorption refers to the existence of a higher concentration of any particular component at the surface of a liquid or a solid phase.
(ii) Adsorption is accompanied by decrease in the (free energy change) of the system when , adsorption equilibrium is said to be established.
(iii) Adsorption is invariably accompanied by evolution of heat, i.e. it is an exothermic process. In other words, DH of adsorption is always negative.
(iv) When a gas is adsorbed, the freedom of movement of its molecules becomes restricted. On account of it decrease in the entropy of the gas after adsorption, i.e. DS is negative.
(v) For a process to be spontaneous, the thermodynamic requirement is that must be negative, i.e. there is decrease in free energy. On the basis of Gibb’s Helmholtz equation, , can be negative if has sufficiently high negative value and has positive value.