CBSE Class 12 Chemistry Surface Chemistry Board Exam Notes

KEY POINTS
 
•  The branch of chemistry which deals with the study of surface phenomena .
•  Adsorption:The phenomenon of attracting and retaining the molecules of a substance at the surface of the solid or a liquid resulting into higher concentration of the molecules on the surface than in the bulk.
•  Adsorbent: The substance where adsorption occurs.
•  Adsorbate: The substance that get adsorbed.
•  Absorption: The phenomenon in which the particles of gas and liquid get uniformly distributed throughout the body of the solid.
•  Desorption: The process of removal of an adsorbed substance from the surface on which it is adsorbed.
•  Sorption: When both absorption and adsorption occur together and are not distinguishable.
•  Mechanism of adsorption : arises due to unbalanced force of attraction on the surface of solid that are r responsible for attracting the adsorbate particles on the surface.
•  The extent of adsorption increases with increase in surface area.
 
Gibbs energy change during adsorption : During adsorption, there is always decrease in residual force i.e., there is decrease in surface energy, which appears as heat. Therefore adsorption is an exothermic process i.e.
CBSE-Class-12 Chemistry Surface Chemistry Board Exam Notes= – ve .
 
CBSE-Class-12 Chemistry Surface Chemistry Board Exam Notes-1
 
¶ Types of Adsorption: physical and chemical adsorption

1. Physical adsorption : When the particles of adsorbate are held to the surface of adsorbent by weak Van der Waals forces,
Characteristics of physical adsorption: Lack of specificity, low enthalpy of adsorption, reversible in nature, no activation energy required,decrease with increase in temperature .
 
2. Chemical adsorption : When the molecules of adsorbate are held to the surface of adsorbent by strong chemical forces.
Characteristics of chemical adsorption: Highly specific in nature, high enthalpy of adsorption, Irreversible in nature, initially it increases with increase in temperature as it needs activation energy, very slow .
 
Adsorption Isotherm: The variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature can be expressed by means of a curve termed as adsorption isotherm.
(Its a plot / curve between extent of adsorption( x/m) and pressure P at constant T).
 
 
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