Question

Which of the following is true in respect of adsorption?
A.$\Delta G < 0;\Delta S > 0;\Delta H < 0$
B.$\Delta G < 0;\Delta S < 0;\Delta H < 0$
C.$\Delta G > 0;\Delta S < 0;\Delta H < 0$
D.$\Delta G > 0;\Delta S > 0;\Delta H > 0$

Answer 1

Hint:Adsorption is known as the accumulation of molecules on the surface of another molecule in bulk. The substance which is said to be adsorbed is known as the adsorbate and the surface on which it is adsorbed is known as the adsorbent.

Complete answer:
Adsorption is the process of formation of a coating or a film of a substance on the surface of another. The substance which is said to be adsorbed is known as the adsorbate and the surface on which it is adsorbed is known as the adsorbent. It is thus referred to as the accumulation of molecules on the surface of another molecule in bulk. There are two types of adsorption which are physical and chemical adsorption. Physical adsorption is known as physisorption which is due to the accumulation of gas on the surface of a solid due to weak Van der Waals’ forces between the adsorbate and the adsorbent. Chemical adsorption is known as chemisorptions in which the accumulation of gas on the surface of a solid due to chemical bonds between the adsorbate and the adsorbent.
Adsorption takes place when change in entropy, change in Gibbs energy and change in enthalpy are negative. Adsorption of gas on a solid surface is an exothermic reaction which produces heat due to decreasing entropy and the gas molecules also decrease the randomness.

Thus, the correct option is (B) where $\Delta G < 0;\Delta S < 0;\Delta H < 0$.

Note:
Adsorption and absorption are processes which may take place simultaneously, this is known as sorption and desorption is the process of removal of an adsorbate from the surface of the adsorbent. Adsorption isotherm is the curve which expresses the variation in the amount of adsorbed gas with pressure at constant temperature and therefore, the curve is referred to as an isotherm.