Compare and contrast the phenomenon of physisorption abd chemisorpion.

Explanation

Characterstics of physical adsorption :
Lack of specificity: physisorption is not specific. In this adsorption the given surface of adsorbent doesent show any perference for a parricular gas as the forces present are varder waal's forces (universal).
nature of adsorbate: The amount of gas adsorbed by a solid depends on the nature of gas.
Easily liquefiable gases are readily adosorbed.
The gas with high critical temperature value is easily liquefied and gets readily adsorbed.
Reversible Nature: physical adsorption is reversible and occurs rapidly at low temperatures.
Surface area of adsorbent: The extent of adsorption increase with increase in surface area of adsorbent.
Finely divided metals and porous substances having large surface area are good adsorbents.
Enthalpy of adsorption : physisorption is an exothermic process but the enthalpy of adsorption is low (20-40 kJ/mole). This is due to the presence of Vander waal's forces.
Chemisroption : if the forces that are responsible for the formation of adsorbate molecules on the source of adsorbent are chemical forvces, the formation of adsorbate molecules on the sorre of adsobent are chemical forces, the adsorbents.
Eg: adsorption of `H_(2)` on Ni -metal surface .
i) High specificity : Chemisorption is highly specific and it will only occur if there is some possibility of chemical bonding between adsorbate and adsorbent .
ii) Irreversibility : Chemisorption involves compound formation and is irreversible in nature.
`to `Chemisorprion is exothermic and inceases with increase with increase of temprature.
iii) Surface area: Chemisorprion increase with increase of the adsorbent.
iv) Enthalpy of adsorption Enthalpy of chemissorprion is high (80-240 kJ/mole).