Question

Why does physisorption decrease with the increase of temperature?

Answer 1

Hint: Physisorption is physical adsorption. This process is an exothermic process. This process depends on the surface area of the adsorbent. Extent of physical adsorption increases with the increase in surface area.

Complete step by step answer:
Physisorption is physical adsorption. This process is an exothermic process. In this process, due to Vander waals forces gas gets accumulated on a solid surface. This process depends on the surface area of adsorbent. As the surface area of adsorbent increases, the rate of this process increases. Extent of physisorption is more in finely divided metal particles or in porous materials. This is an exothermic process that means heat is evolved in this process. Le chatelier’s principle is used in predicting the effect of change in temperature or pressure on chemical equilibrium. According to this principle if some change is made in the state of the system, the system will change itself accordingly so that the effect of change of state is negligible. In case of physical adsorption, heat is evolved. This means the temperature of the surrounding will increase and we are also increasing temperature. So, according to le chatelier’s principle the system will move in that direction in which temperature will decrease. Therefore the reaction will move towards backward direction in order to decrease the temperature (as reaction is exothermic in forward direction). So, the rate of physisorption decreases with increase in temperature.


Note:
Le chatelier’s principle is very helpful in predicting the equilibrium of reactions. If we will increase the temperature or pressure of the system then the system will shift itself accordingly in that direction in which the effect of change of temperature or pressure will be minimum.