Which of the following is incorrect about chemical adsorption?

It's not specific

The correct answer is option 4. It's not specific.

Let us break down each statement about chemical adsorption (chemisorption) to explain why one of them is incorrect:

1. It's monolayered

In chemisorption, the adsorbate forms a chemical bond with the surface of the adsorbent. Since these bonds are specific and involve particular sites on the surface, chemisorption typically results in a monolayer. Once all the available surface sites are occupied by adsorbed molecules, no additional layers can form. Therefore, this statement is correct.

2. \(\Delta H^o > 40 \, \text{kJ/mol}\)

The enthalpy change (\(\Delta H^o\)) for chemisorption is usually quite high because it involves the formation of strong chemical bonds. The energy associated with chemisorption is typically much greater than 40 kJ/mol, often in the range of 80-200 kJ/mol or more. This reflects the energy required to form or break chemical bonds, so this statement is also correct.

3. It's irreversible

Chemisorption is often considered irreversible because the chemical bonds formed between the adsorbate and the surface are strong. Reversing the adsorption (desorption) would require breaking these bonds, which typically requires a significant amount of energy. Therefore, this statement is correct.

4. It's not specific

Chemisorption is highly specific. The process depends on the chemical nature of both the adsorbent and the adsorbate. Only certain molecules with the appropriate chemical properties can form bonds with specific sites on the adsorbent's surface. This specificity differentiates chemisorption from physisorption, which is generally non-specific and based on weaker van der Waals forces.

Why This is Incorrect: Saying "It's not specific" is incorrect because chemisorption is indeed a specific process. The ability of a molecule to adsorb onto a surface via chemisorption depends on the specific chemical interactions between the adsorbate and the adsorbent.

Conclusion
The incorrect statement is Option 4: It's not specific. Chemisorption is specific because it involves the formation of chemical bonds that depend on the nature of the adsorbate and the adsorbent.