Why the rate of chemical adsorption first increases and then decreases with rise of temperature ?

Explanation

Chemical adsorption involves a chemical reaction between adsorbent and adsorbate. As we know, the rate of a chetnical reaction always increases with increase in temperature, because the heat added provides the activation energy. This explain why rate of chemical adsorption first increases. With increase in temperature, desorption involves breaking of bonds and breaking of bonds requires energy. As the temperature rises furthers the additional amount of heat added is used for breaking the bonds first formed leading to desorption (desorption is reverse of absorption). This increases in the rate of desorption with increases in temperature lowers the rate of adsorption.