Question

Explain the difference between Physisorption and Chemisorption.

Hint:

Physisorption = weak, reversible, multilayer; Chemisorption = strong, specific, monolayer adsorption.

Answer 1

Concept: Adsorption is the accumulation of molecules on the surface of a solid or liquid. Based on the nature of forces involved, adsorption is classified into physisorption and chemisorption.
Step 1: Physisorption. Physisorption (physical adsorption) occurs due to weak intermolecular forces such as van der Waals forces.

• Low enthalpy of adsorption
• Reversible in nature
• Occurs at low temperatures
• Multilayer adsorption possible
• No specific surface requirement

Step 2: Chemisorption. Chemisorption (chemical adsorption) involves formation of strong chemical bonds between adsorbate and adsorbent.

• High enthalpy of adsorption
• Usually irreversible
• Occurs at higher temperatures
• Only monolayer adsorption
• Highly specific in nature

Step 3: Key Differences.

• 
  Nature of forces: Physisorption — weak van der Waals forces; Chemisorption — strong chemical bonds.
• 
  Reversibility: Physisorption is reversible; chemisorption is usually irreversible.
• 
  Temperature dependence: Physisorption favored at low temperature; chemisorption at higher temperature.
• 
  Layer formation: Physisorption forms multilayers; chemisorption forms a monolayer.

Conclusion: Physisorption and chemisorption differ mainly in the strength of interaction and reversibility, with physisorption being weak and reversible and chemisorption being strong and specific.