Question

Which of the following statement(s) is/are false about the properties of adsorption?

• A. Both physisorption and chemisorption are non-specific in nature
• B. Enthalpy of adsorption for physisorption is around $20-40kJ/mol$
• C. All gases undergoes chemisorption with adsorbent
• D. Both physisorption and chemisorption favour low temperature

Answer 1

Answer: (A), (C), (D)

Both physisorption and chemisorption favour low temperature

1. Specificity of adsorption:
Physisorption is non-specific because the adsorbate and adsorbent are held by weak van der Walls' forces of attraction. So it is non-specific.
Chemisorption is more specific because the adsorbate and adsorbent are held by chemical bond.

2. Enthalpy of adsorption:
Due to weak van der Waal's force, the enthalpy of adsorption for physisorption is less and it is about $20-40kJ/mol$
Due to chemical bonds, the enthalpy of adsorption for chemisorption is greater and it is about $80-240kJ/mol$

3. Nature of gas:
Gases which can react with the adsorbent only shows chemisorption.

4. Physisorption is exothermic process so by Le- Chatelier's principle low temperature is favourable for it.

Chemisorption is also exothermic process but it has high activation energy, so to form chemical bonds it require high temperature to meet the required activation energy. Hence, high temperature is favoured for chemisorption.

Hence, statements (a), (c) and (d) are false.