Classification of adsorption
Adsorption can be classified into two categories as described below,
(1) Depending upon the concentration : In adsorption the concentration of one substance is different at the surface of the other substance as compared to adjoining bulk or interior phase.
(i) Positive adsorption : If the concentration of adsorbate is more on the surface as compared to its concentration in the bulk phase then it is called positive adsorption.
Example : When a concentrated solution of KCl is shaken with blood charcoal, it shows positive adsorption.
(ii) Negative adsorption : If the concentration of the adsorbate is less than its concentration in the bulk then it is called negative adsorption.
Example : When a dilute solution of KCl is shaken with blood charcoal, it shows negative adsorption.
(2) Depending upon the nature of force existing between adsorbate molecule and adsorbent
(i) Physical adsorption : If the forces of attraction existing between adsorbate and adsorbent are Vander Waal's forces, the adsorption is called physical adsorption. This type of adsorption is also known as physisorption or Vander Waal's adsorption. It can be easily reversed by heating or decreasing the pressure.
(ii) Chemical adsorption : If the forces of attraction existing between adsorbate particles and adsorbent are almost of the same strength as chemical bonds, the adsorption is called chemical adsorption. This type of adsorption is also called as chemisorption or Langmuir adsorption. This type of adsorption cannot be easily reversed.
Comparison between physisorption and chemisorption
|
Physisorption
(Vander Waal's adsorption)
|
Chemisorption
(Langmuir adsorption)
|
|
Low heat of adsorption usually in range of 20-40 kJ/mol
|
High heat of adsorption in the range of 50-400 kJ/mol
|
|
Force of attraction are Vander Waal's forces.
|
Forces of attraction are chemical bond forces.
|
|
It is reversible
|
It is irreversible
|
|
It is usually takes place at low temperature and decreases with increasing temperature.
|
It takes place at high temperature.
|
|
It is related to the case of liquefication of the gas.
|
It is not related.
|
|
It forms multimolecular layers.
|
It forms monomolecular layers.
|
|
It does not require any activation energy.
|
It requires high activation energy.
|
|
High pressure is favourable. Decrease of pressure causes desorption
|
High pressure is favourable. Decrease of pressure does not cause desorption.
|
|
It is not very specific.
|
It is highly specific.
|
Email based Chemistry assignment help - homework help at Expertsmind
Are you searching chemistry expert for help with Classification of adsorption questions? Classification of adsorption topic is not easier to learn without external help? We at www.expertsmind.com offer finest service of Chemistry assignment help and chemistry homework help. Live tutors are available for 24x7 hours helping students in their Classification of adsorption related problems. We provide step by step Classification of adsorption question's answers with 100% plagiarism free content. We prepare quality content and notes for Classification of adsorption topic under chemistry theory and study material. These are avail for subscribed users and they can get advantages anytime.
Why Expertsmind for assignment help
- Higher degree holder and experienced experts network
- Punctuality and responsibility of work
- Quality solution with 100% plagiarism free answers
- Time on Delivery
- Privacy of information and details
- Excellence in solving chemistry queries in excels and word format.
- Best tutoring assistance 24x7 hours