n.
Capability of a solid substance (adsorbent) to attract to its surface molecules of a gas or solution (adsorbate) with which it is in contact.
Physical adsorption depends on van der Waals forces of attraction between molecules and resembles condensation of liquids. In chemical adsorption (often called chemisorption; see catalysis ), the gas is held to the surface by chemical forces specific to the chemicals involved, and formation of the bond may require an activation energy .