In chemisorption, the extent of adsorption x/m increases first with the rise in temperature because the chemical reaction involved in chemisorption requires activation energy initially i.e heat is absorbed for activation which causes increase in adsorption but later on chemisorption decreases with the rise in ...

Chemisorption and Adsorption

Chemisorption is a type of adsorption in which the adsorbate molecules or atoms are bonded to the surface of the adsorbent by chemical bonds. This process involves the formation of new chemical bonds between the adsorbate and adsorbent, resulting in the adsorption of the adsorbate onto the surface of the adsorbent.

Adsorption is the process by which a substance, known as the adsorbate, accumulates on the surface of another substance, known as the adsorbent. The adsorbate molecules or atoms adhere to the surface of the adsorbent through weak intermolecular forces such as Van der Waals forces, electrostatic interactions, or hydrogen bonding.

Exothermic Nature of Adsorption

When chemisorption occurs, there is a release of energy in the form of heat. This is because the formation of chemical bonds between the adsorbate and adsorbent is an exothermic process. The energy released during chemisorption is often higher than the energy required to break the bonds in the adsorbate molecules.

Adsorption Decreases after Increase

The decrease in adsorption after an initial increase in chemisorption can be attributed to the exothermic nature of adsorption. As the adsorbate molecules or atoms bond to the surface of the adsorbent, heat is released. This heat can cause the desorption of some of the adsorbate molecules from the surface of the adsorbent.

The release of heat during chemisorption can increase the mobility of the adsorbate molecules, allowing them to overcome the attractive forces holding them to the surface of the adsorbent. As a result, some of the adsorbate molecules may desorb from the surface, leading to a decrease in the overall adsorption.

Endothermic Nature of Adsorption

In contrast, if the adsorption process is endothermic, an increase in adsorption would be expected with an increase in temperature. This is because an endothermic process absorbs heat from the surroundings, which provides the energy required for adsorption to occur. In such cases, an increase in temperature would increase the energy available for adsorption, leading to an increase in the overall adsorption.

Weak Force of Van der Waals

The weak force of Van der Waals alone is not the primary factor responsible for the decrease in adsorption after an initial increase in chemisorption. While Van der Waals forces are important in adsorption processes, chemisorption involves the formation of stronger chemical bonds between the adsorbate and adsorbent. The release of energy during chemisorption leads to desorption, rather than the weak Van der Waals forces.