Adsorption

Chemistry

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Adsorbate

A material that has been or is capable of being adsorbed is known as adsorbate.
e.g Oxygen molecule adsorbed on cobalt. Here oxygen is adsorbate.

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Adsorbent

The substance on which adsorbate is adsorbed is called adsorbent. Major types of adsorbents in use are: activated alumina, silica gel, activated carbon, molecular sieve carbon, molecular sieve zeolites and polymeric adsorbents. Most adsorbents are manufactured (such as activated carbons), but a few, such as some zeolites, occur naturally.

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Mechanism of adsorption

Adsorption occur when the surface particles of the adsorbent experience the unbalanced attractive forces from the bulk, but on the surface the particles are not surrounded by atoms or molecules from all side. Hence, they possess unbalanced attractive forces. These forces of the adsorbent are responsible for attracting the adsorbate particles on its surface.
Adsorption increase with increase in surface area per unit mass of the adsorbent at a given temperature and pressure. 

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Exothermic nature of adsorption and the entropy change

When adsorption takes place, surface energy decreases. This appears in the form of heat of adsorption. Hence, adsorption is invariably an exothermic process,i.e is always negative.

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Difference between adsorption and absorption

Adsorption
Absorption
It is a surface phenomenon
It is a bulk phenomenon
The concentration on the surface of adsorbent is different from that in the bulk
The concentration is same throughout
Its rate is high in the beginning and then decreases
It remains same throughout the process

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Adsorption

Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. They are of two types: Physisorption and Chemisorption, e.g., oxygen molecules (red) adsorbed on a bimetallic surface of platinum (purple) and cobalt (green).
  • A material that has been or is capable of being adsorbed is known as adsorbate.
  • Example- Oxygen molecule adsorbed on cobalt. Here oxygen is adsorbate.
  • The substance on which adsorbate is adsorbed is called adsorbent
  • Major types of adsorbents in use are activated alumina, silica gel, activated carbon, molecular sieve carbon, molecular sieve zeolites, and polymeric adsorbents.


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Sorption

When both adsorption and absorption take place simultaneously. The term sorption is used.
e.g: Dyes get adsorbed as well as absorbed in the cotton fibres.

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Factors affecting adsorption of gases by solids

  • Nature and surface area of the absorbent
  • Nature of the gas being adsorbed
  • Temperature
  • Pressure
  • Activation of the solid adsorbent

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Heat of adsorption

The amount of heat evolved when 1 mole of the gas is adsorbed on the adsorbent is called heat of adsorption.

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Types of Adsorption

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Adsorption Isotherms

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Applications of Adsorption

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