Test: Adsorption, Adsorption isotherms - JEE MCQ

Van der Waal force ↑ adsorption ↑

to

(a) The extent of adsorption increases with an increase in temperature is an incorrect statement because an increase in temperature reduces the interaction between the absorbate molecules and adsorbent molecules.
(b) The extent of adsorption decreases with an increase of surface area of the adsorbate is also an incorrect statement as adsorption surface area of adsorbate.
(c) The extent of adsorption decreases with an increased in temperature.

Thus, is the correct statement.
(d) The extent of adsorption does not depend on amount of solute in solution.
This is also an incorrect statement because :

where, amount of adsorbent , adsorbed on given mass of adsorbate and an integer. Thus, plot of gives a straight line upward slope.
Hence, option (c) is the correct answer.

For adsorption and for a spontaneous change hence should be highly negative which is clear from the equation

So if is highly negative will also be

On the basis of equation, ΔG=ΔH−TΔS can be negative if ΔH has sufficiently high negative value as −TΔS is positive. Thus, in adsorption which is a spontaneous process.
ΔS is negative, ΔH is sufficiently negative and as a result ΔG is also negative

The physical adsorption (ie, physisorption) is an exothermic process, so on the basis of Le-Chatelier principle increasing of temperature is favourable towards a direction in which heat is absorbed, so the rate of physisorption increases with decrease of temperature.