Explain the terms absorption, adsorption and sorption. Describe the different types of adsorption.

Explanation

Absorption : The uniform distribution of a substance through out the bulk of the solid substance is known as absorption.
Eg : Chalk stick dipped in ink.
Adsorption : The accumulation (or) concentration of a substance on the surface rather than in the bulk of solid (or) liquid is known as adsorption.
Eg : Adsorption ‹›f gases like `O_(2)`, H ,` Cl_(2)` etc., on charcoal
Sorption : In case of some substances both adsorption and absorption takes place. This phenomenon is called sorption.
Tyes of adsorption : On the basis of forces present between adsorbate and adsorbent molecules, adsorption classified into two types
1) Physisorption , 2) Chemisorption
1) Physisoption : If the forces that are responsible for the adsorption of adsorbate molecules on the surface of the adsorbent are weak vander waal's for the adsorption is known as pysisorption.
Eg: Adsorption of `H_(2) ` on `O_(2)` on charcoal.
Characteristics :
` to `It is a weak adsorption.
`to` Enthalpy of adsorption is low (20 - 40 KI /Mole ).
`to` It is reversible and occurs rapidly.
`to` It decrease with increase in temperature.
`to `It increase with increase in pressure. It is multilayered and not specific.
2) Chemisorption : If the forces that are responsible for the formation of adsorbate molecules on the surface of adsorbent are chemical forces, the adsorbtion is called chemisorption. Eg: Adsorption of `H_(2) ` on Ni-metal surface.
Characteristics :
`to` It is a strong adsorption.
`to ` Enthalpy of adsorption of high (80 - 240 KI / mole).
`to ` It is irreversible and occurs slowly.
`to` It increases with increase of temperature and finally decrease.
`to` Pressure has no effect on chemisorption.
`to` It is unilayered and specific.