Understanding Chemisorption

Chemisorption is the other name for chemical adsorption which is a chemical process. The process of chemisorption is related to chemical bonds that are formed between particular surface locations (active sites) on materials and adsorbate molecules. This is the defining feature of chemisorption. The creation of electronic bonds is due to the interactions between a substrate surface and the adsorbate molecules. In chemisorption, the electronic bond formed is either covalent or ionic. The process of adsorption is essentially attaching molecules, atoms, or ions from a liquid or a gas to some material surface. This process is not similar to absorption. 

Chemisorption

Chemisorption is a surface phenomenon. It is the result of surface energy. Atoms available on the surface of an adsorbent do not have surrounding adsorbent atoms completely so can attract adsorbates. This is different from regular bulk materials since, in it, the constituent for an electronic bond is fulfilled by separate atoms present in the material itself. Other sorption processes like chemisorption are ionic exchange and chromatography. The chemisorption process is used widely in chemical systems, especially in heterogeneous catalysts, a part of the air conditioning process, water purification, synthetic resins, and adsorption chillers. Chemisorption is a natural process as well. An example of chemisorption includes corrosion. Chemisorption is a much stronger chemical phenomenon than physical adsorption. Physical adsorption occurs on all surfaces provided that the temperature and the pressure are conducive to it. Chemisorption however does not happen everywhere but only occurs at certain active sites on the material surface and stops happening once there is no longer a direct contact. This is why chemisorption is not a multi-layered process but a singular layer one. 

Chemical Adsorption

Chemical adsorption is important for measuring the chemical and physical properties of certain materials that are involved in reaction or process performance in industries. Chemisorption helps in determining active sites in the material which in turn will help in understanding how to increase the rate of catalyzation. It also helps in determining the oxidation or reduction temperatures of certain materials. It is predominantly used in petroleum and oil industries as well as in petrochemicals. The key difference between absorption and adsorption is that the former involves including atoms or molecules in a bulk, however adsorption is an accumulation of ions or atoms or molecules at specific sites on the surface. 

Characteristics of Chemisorption

Chemisorption is an exothermic process. This process however is not fast due to the activation having high energy. The characteristics of Chemisorption are:

• It is irreversible – It is a chemical phenomenon where chemical bonds are formed and these bonds are not easy to break.
• It has high specificity- Its high specificity depends on the interactions happening between the adsorbent and the adsorbate. 
• It increases when the pressure is increased.
• It is directly proportional to temperature. 
• It is directly proportional to the adsorbent’s surface area. 

Physisorption

The opposite of chemical adsorption or chemisorption is physisorption or physical adsorption. Here, gas is adsorbed into a solid in a non-specific way. There are no specific preferences observed due to van der Waals universal forces. It is also a reversible process and has a low enthalpy rate (20-40 kJ mol-1). 

Conclusion

In chemistry, sorption includes the phenomena of adsorption and absorption. In chemisorption, analyses are performed based on dynamic or static flow methods. Pulse chemisorption is a particularly strong type of chemisorption that is used in strong active sites. Chemisorption is used in experiments such as first-order kinetics ( heat desorption), and esoteric heat desorption.