Question

Extent of physisorption of a gas increases with:

• A. increase in temperature
• B. decrease in temperature
• C. decrease in surface area of adsorbent
• D. decrease in strength of van der Waals forces

Answer 1

The correct option is B decrease in temperature

• If accumulation of gas on the surface of a solid occurs on account of weak van der Waals’ forces, the adsorption is termed as physical adsorption or physisorption.
  

Various characteristics of Physisorption are-

• It arises because of van der Waals’ forces.
• It is not specific in nature.
• It is reversible in nature.
• It depends on the nature of gas. More easily liquefiable gases are adsorbed readily.
• Enthalpy of adsorption is low ($20-40$ $kJ$ $mo{l}^{-1}$).
  
• Low temperature is favourable for adsorption. It decreases with increase of temperature.
  
• No appreciable activation energy is needed.
  
• It depends on the surface area. It increases with an increase of surface area.
  
• It results into multimolecular layers on adsorbent surface under high pressure.