What is Adsorption?
Adsorption is a surface phenomenon. The phenomenon of a higher concentration of any molecular species at the only surface than in the bulk of a solid is called adsorption.
What is Adsorbent?
The solid can take up a gas or vapour or a solute from a solution known as an adsorbent.
What is Adsorbate?
The gas, vapour, or solute held to the surface of the solid is called adsorbate.
What is Absorption?
Absorption is a bulk phenomenon. The substance is uniformly distributed throughout a solid or liquid is called absorption.
What is Sorption?
The process in which both adsorption and adsorption take place simultaneously is called sorption.
What is chemisorption?
The chemical process involves the chemical interaction between the adsorbent’s surface atoms and the adsorbate’s atoms. This type of adsorption is called chemisorption.
Physical adsorption occurs only at very low temperatures falling below the boiling point of the adsorbate. Chemisorption can occur at all temperatures.
The magnitude of chemisorption increase with temperature rise. The importance of a chemical reaction in a given time increases with temperature rise. On the other hand, physisorption decreases with temperature rise.
In chemisorption, the heat evolved is very high, generally between 40-400 kJ mol-1, in many chemical reactions. The heat evolved in physisorption is low, between 4-40 kJ mol-1.
Chemisorption is irrelevant as the gas adsorbed cannot be recovered from the adsorbent by lowering the system’s pressure at the same temperature. However, physisorption is reversible as the gas adsorbed can quickly recover from the adsorbent by reducing the system’s pressure at the same temperature.
Chemical forces operate within short distances only, and chemisorption does not extend beyond a monolayer of gas molecules or atoms on the surface of the solid. Physisorption may extend beyond a monolayer.
In physisorption, the adsorbate molecules are held by comparatively weak van der Waals forces. In this category, the activation energy of desorption is very low. In chemisorption, the adsorbate molecules are carried by relatively strong forces. And the activation energy of desorption is very high.
