Chemisorption requires high activation energy. So, it is referred to as activated adsorption. In chemisorption, the graph of adsorption first increases and then decrease with an increase in temperature. When adsorption isobar is plotted, the graph initial increase due to heat supplied, which acts as activation energy required in chemisorption. But later it decreases, due to exothermic nature of adsorption at equilibrium position.