Question

Explain the term physisorption.

Answer 1

Physisorption, or physical adsorption, is the process where gas molecules adhere to the surface of a solid due to weak van der Waals forces. It is non-specific, meaning any gas can be adsorbed this way. Physisorption is reversible, so the gas can be removed by lowering pressure or increasing temperature. The heat released during physisorption is low, about 20–40 kJ/mol. It often forms multiple layers of adsorbed gas on the solid surface. Physisorption decreases with rising temperature because these weak forces weaken, but it increases with higher gas pressure. Gases that are easily liquefiable with higher critical temperatures tend to be adsorbed more readily. In brief, physisorption involves weak physical forces and does not form chemical bonds between the gas and solid surface.