Question

Write any two characteristics of chemisorption.

What are the important characteristics of chemical adsorption?

Answer 1

1. Chemisorption is highly specific in nature. It occurs only if there is a possibility of chemical bonding between the adsorbent and the adsorbate.
2. Like physisorption, chemisorption also increases with an increase in the surface area of the adsorbent.
3. Chemical adsorption usually involves a chemical change and is therefore irreversible in most cases.
4. The heat of adsorption in chemisorption is higher (about 80–240 kJ/mol) compared to physical adsorption, because chemisorption involves the formation of chemical bonds.
5. Chemisorption is strictly monolayered; gas molecules once adsorbed on the surface cannot form further layers.
6. The extent of chemisorption first increases and then decreases with the rise in temperature because of the activation energy barrier.
7. Chemisorption increases with an increase in pressure, since higher pressure helps in bringing the gas molecules closer to the adsorbent surface to form chemical bonds.
8. The extent of chemisorption depends on the capacity of the gas to form valence bonds with the surface of the adsorbent, not on the critical temperature of the gas.