The key difference between adsorption and desorption is that adsorption refers to the process by which some solids hold the molecules of a gas or liquid or solute as a thin film, whereas desorption refers to the release of an adsorbed substance from a surface.
Adsorption and desorption are chemical processes that are opposite to each other. We can observe these processes in many biological, physical and chemical systems. It can occur naturally or we can perform adsorption and desorption for chemical experiments.
CONTENTS
1. Overview and Key Difference
2. What is Adsorption
3. What is Desorption
4. Side by Side Comparison – Adsorption vs Desorption in Tabular Form
5. Summary
What is Adsorption?
Adsorption refers to the process by which some solids hold molecules of a gas or liquid or solute as a thin film. Therefore, it is the process of adhesion of molecules onto a surface. The substance that is going to attach to the surface is called the “adsorbate”. The substance which has the surface for the absorption is called the “adsorbent”. The adsorption process is a surface phenomenon. Desorption is the reverse of the adsorption.
Figure 01: Activated Carbon is a Good Adsorbent
Furthermore, adsorption is a consequence of surface energy. We can classify adsorption into two groups as chemisorption and physisorption. Chemisorption occurs due to covalent bonding between adsorbent and adsorbate while physisorption occurs due to weak Van der Waal forces. However, sometimes adsorption occurs due to electrostatic attraction between adsorbent and adsorbate.
Usually, the adsorption of gases and solutes is described through isotherms. It describes the amount of adsorbate on the adsorbent as a function of the pressure of the gas or its concentration at a constant temperature.
What is Desorption?
Desorption refers to the release of an adsorbed substance from a surface. This is the opposite process of sorption. Desorption occurs in a system having a state of sorption equilibrium between the bulk phase and adsorbing surface. Therefore, if we lower the concentration of the substance in the bulk phase, some of the sorbed substance changes to the bulk state. In chromatography, the desorption is the process that aids the movement of the mobile phase.
After desorption occurs, the desorbed substance remains on the substrate nearly indefinitely if the temperature remains low. However, when the temperature rises, desorption is likely to occur. The general equation for the rate of desorption is as follows.
R = rNx
Where R is the rate of desorption, r is the rate constant, N is the concertation of the adsorbed material and x is the kinetic order of the reaction. There are a few different ways desorption can occur. For example, thermal desorption, reductive desorption, oxidative desorption, electron-stimulated desorption, etc.
What is the Difference Between Adsorption and Desorption?
Adsorption and desorption are chemical processes that are opposite to each other. The key difference between adsorption and desorption is that adsorption refers to the process by which some solid holds molecules of a gas or liquid or solute as a thin film whereas desorption refers to the release of an adsorbed substance from a surface. Moreover, adsorption involves the formation of covalent bonds or attachment through Van der Waal forces while desorption involves the breakdown of covalent bonds or attractive forces.
The following infographic summarizes the difference between adsorption and desorption.
Summary – Adsorption vs Desorption
Adsorption and desorption are chemical processes that are opposite to each other. The key difference between adsorption and desorption is that adsorption refers to the process by which some solid holds molecules of a gas or liquid or solute as a thin film, whereas desorption refers to the release of an adsorbed substance from a surface.
Reference:
1. Helmenstine, Anne Marie. “What Adsorption Means in Chemistry.” ThoughtCo, Aug. 7, 2019, Available here.
Image Courtesy:
1. “Activated Carbon” By Self (en:User:Ravedave) – Self (en:User:Ravedave) (CC BY 2.5) via Commons Wikimedia