The process is unique in that it will only occur if a chemical bond is formed between the adsorbent and the adsorbate. In nature, the process is irreversible. It's an exothermic reaction, which means the temperature rises as a result of the reaction. In chemical adsorption the rate of adsorption is slow when the temperature is low, but as the pressure rises, it happens faster. Chemisorption, like physisorption, is directly proportional to surface area and so increases as surface area grows. The enthalpy is high because the process requires chemical bond formation. It necessitates a specific amount of activation energy.