in chemisorption , why x/m increases and then decreases with rise in temperature ?

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 temperature due to exothermic nature of chemisorption.