Class 12 Chemistry Surface Chemistry Adsorption and Absorption

Adsorption and Absorption


The dirt staying on the surface of the skin as a layer is termed as adsorbtion.

Now consider applying soap solution to the shirt containing dirt.  The soap solution is absorbed by the fabric and does not stay on the fabric as a layer. This is called absorption.


Adsorption is the phenomenon of attracting and retaining molecules of a substance on the surface of a solid (or liquid) resulting as a higher concentration of molecules only on the surface.

  • Adsorbent- the surface on which adsorption takes place
  • Adsorbate- the substance which is adsorbed

Example- Water vapour adsorbed by silica gel

  • Adsorbent- Silica gel
  • Adsorbate- Water vapour

Differences between Adsorption and Absorption



Surface phenomenon- concentration of the adsorbate increases only on the surface

Bulk phenomenon- concentration is uniform throughout the solid

Exothermic process- heat is released

Endothermic process- heat is absorbed

It is favoured by low temperature

It is not affected by temperature

Eg- Chalk stick dipped in ink adsorbs the colour of the ink but when you break the piece of chalk, its core still remains white

Eg- When anhydrous CaCl2 absorbs water vapour, it becomes wet and pasty



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