Question

Which of the following statement is not correct?

• A. Adsorption energy for chemical adsorption is generally greater than that of physical adsorption
• B. Physical adsorption is due to van der Waal forces
• C. Physical adsorption decreases at high temperature and low pressure
• D. Physical adsorption is irreversible

Answer 1

Answer: (D)

Physical adsorption is irreversible

Answer 2

Adsorption is a process of deposition of molecules on the surface of another substance. It occurs in two ways:

• Physisorption
• Chemisorption

Physical adsorption is a reversible process. It occurs due to the non-covalent attraction between adsorbate and adsorbent. In Physisorption, the two molecules are held together by weakintermolecular forcesi.e. van der Waal forces, hence it is reversible. With increase in temperature, physical adsorption of substances decreases. Since in physisorption, molecules are held together by weak forces of attraction, therefore its energy of adsorption is also low as compared to chemisorption. Hence, only the fourth statement is incorrect here.

In Chemisorption, the adsorbate and adsorbent are held together by strong covalent bonds, therefore this process is irreversible and requires high adsorption energy.