Adsorption and Colloids — Chemistry STD 11 Science — Question

When the adsorbent such as gas molecules are accumulated at the surface of a solid on account of weak van der Waals forces, the adsorption is termed as physical adsorption or physisorption.

Characteristics:

• The van der Waals forces involved in physical adsorption are similar to forces causing condensation of gas into liquid. Thus, heat is released in physisorption.
• The heat released during physisorption is of the same order of magnitude as heat of condensation.
• Due to weak nature of van der Waals forces, physisorption is weak in nature.
• The adsorbed gas forms several layers of molecules at high pressures.
• The extent of adsorption is large at low temperatures.
• The equilibrium is attained rapidly.
• Physisorption is readily reversed by lowering of pressure of gas or by raising temperature.