Question

Extent of physisorption of a gas increases with

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

Answer 1

Solution

The correct option is a B) decrease in temperature

Explanation

Physisorption is exothermic by nature. So, the rate of physisorption of a gas increases with a decrease in temperature and low temperature is favourable for adsorption. on the increasing temperature, they get desorbed easily. It is because, in physisorption, particles are held to the surface by weak van der Waals’ force of attraction.

Characteristics of Physisorption

• It is due to the formation of van der Waals forces.
• It is reversible in nature.
• Physisorption is not specific in nature.
• It has low adsorption enthalpy, nearly 20 to 40 kJ/mol.
• It favours low temperature.
• Physisorption decreases with increase in temperature.
• It results in a multimolecular layer.
• Activation energy is less in physisorption.

Hence, option ( B ) is correct.

Related questions

1. What is Vander waal force ?
2. Why is chemisorption referred to as activated adsorption?
3. What is the difference between physisorption and chemisorption?