Question

Which of the following is not a characteristic of chemisorption?
A.Adsorption is reversible
B.$\Delta H$ is of the order of $400KJ$
C.Adsorption is specific
D.Adsorption increases with increase of surface area

Answer 1

We need to understand the definition along with the characteristics of chemisorption. Chemisorption is also known as chemical adsorption. Chemisorption is a process that occurs when adsorbate molecules form a chemical connection with certain surface areas on a substance known as active sites. Chemisorption is mostly used to assess the amount of accessible active sites in order to accelerate or catalyse chemical processes.

Complete answer:
Chemisorption is a type of adsorption in which a chemical reaction occurs between the surface and the adsorbate. At the adsorbent surface, new chemical bonds are formed. Macroscopic events, such as corrosion, are prominent examples, as are subtler effects related with heterogeneous catalysis, in which the catalyst and reactants are in distinct phases. The adsorbate's intense contact with the substrate surface results in the formation of novel forms of electronic bonds.
Chemisorption has a number of properties, including:
Chemisorption is extremely selective, and it will only occur if there is a potential of chemical interaction between adsorbent and adsorbate.
It is irreversible in nature.
Surface area: As the adsorbent's surface area rises, so does chemisorption.
Enthalpy of adsorption: The enthalpy of chemisorption is high ($80 - {\text{ }}240kJmo{l^{ - 1}}$) because it includes the creation of chemical bonds.

Hence, the correct option is option A.

Note:
It must be noted that in contrast to chemisorption, physisorption preserves the chemical species of the adsorbate and the surface. The energetic threshold distinguishing the binding energy of "physisorption" from that of "chemisorption" is generally believed to be around 0.5 eV per adsorbed species. The nature of chemisorption can vary considerably due to specificity, depending on the chemical identity and surface structural characteristics. In chemisorption, the link between the adsorbate and the adsorbent can be ionic or covalent.