ABSTRACT
Adsorption is a term used to describe the existence of a solute concentration (dissolved substance) at the interface between a fluid and a solid higher than that present in the fluid. Adsorption is sometimes classified as physical adsorption or chemisorption. In physical adsorption the van der Waals forces act between the adsorbed compound and the adsorbing substance. During the process, the heat liberated is between 8 and 21 kJ/mol. These energies fall in the range of diffusion-controlled processes. There is no activation energy, but electrostatic forces can intervene. In chemisorption, there is chemical binding between the adsorbent and the adsorbed substance. This leads to modifications in the molecular structures, so that the liberated heat ranges around 40 to 200 kJ/mol, resulting in activation energy. Consequently, chemisorption takes place more quickly at higher temperatures. Since physical adsorption and chemisorption are both exothermic processes, adsorption is quantitatively favored at lower temperatures, according to the principle of Le Chatelier-Van’t Hoff.
