Question

How are physisorption and temperature related?

Answer 1

Adsorption is always an exothermic process$\left( \Delta H=negative \right)$. With this hint, you can answer this question.

Complete answer:
-Let us understand physisorption and the factors affecting it, physisorption is a type of adsorption in which the Van der waal force is involved between the adsorbate and the adsorbent. It is also called Physical adsorption or Van der waal adsorption.
-As we know, Van der waal force is a weak intermolecular force, so the enthalpy of adsorption in physisorption is low. It is around $-\left( 20-40 \right)KJmo{{l}^{-1}}$. The negative sign indicates that this much amount of energy/heat is released during the adsorption.
-As mentioned in the hint that adsorption is always an exothermic process because the adsorbate gets attracted to the adsorbent in adsorption and as we know attraction always lowers the energy of the system which means it is going to be an exothermic process. So according to Le-Chatelier’s principle, the extent of physisorption will decrease with increase in temperature. That’s why physisorption is favourable at low temperature.

Note:
Some important points about physisorption are:
-Any gas can participate in physisorption as any gas can develop van der waal force. So there is no specificity in physisorption.
-Physisorption is a reversible process that means if a gas is adsorbed, it can be desorbed.
-Activation energy in physisorption is almost zero as not much of an energy is required in developing van der waal force and due to less activation energy it is much faster than the chemisorption.