Question

Which of the following are not characteristics of chemisorption?
(A) Adsorption is specific.
(B) Heat of adsorption is of die order of $ 200\text{ }KJ\text{ }mo{{l}^{-1}} $
(C) Adsorption is irreversible.
(D) Adsorption may form multimolecular layers.

Answer 1

Hint: We know that the chemisorption is one type of adsorption which involves a chemical reaction between the surface and the adsorbate. Generated new chemical bonds are at the adsorbent surface.

Complete Step By Step Answer:
As we know that Chemisorption involves the transfer, exchange, or sharing of electrons between adsorbate and adsorbent atoms/molecules and the adsorption of adsorbates on adsorbents is due to the formation of chemical bonds between them. It is irreversible in nature because the chemical bond formed is difficult to break. Chemisorption’s process is directly proportional to surface area and thus increases with an increase in surface area with an increase in chemisorption.
Also, the heat or enthalpy of chemisorption is high $ (80-240\text{ }KJ\text{ }mo{{l}^{-1}}). $ The chemisorption process involves chemical bond formation hence the enthalpy is high. The chemisorption process requires a certain energy of activation. Chemisorption is an exothermic process and the process is accompanied by an increase in temperature. The chemisorption process occurs slowly at low temperatures and occurs at a higher rate with an increase in pressure. Thus, chemisorption doesn’t form multimolecular layers.
Therefore, the correct answer is option D.

Note:
Don’t get confused between chemisorption and physisorption. Physisorption is called physical adsorption, physisorption is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption.