Key notes for class 12 Chemistry chapter 05 Surface Chemistry. it includes revision notes such as The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed as adsorption. It is a surface phenomenon. The concentration of adsorbate increases only at the surface of the adsorbent. It is the substance present in bulk, on the surface of which adsorption is taking place. It is the substance which is being adsorbed on the surface of another substance. It is the process of removing an adsorbed substance from a surface on which it is adsorbed.