Directions: In the following questions, A statement of Assertion (A) ...
∆G = ∆H – T∆S Gibbs Free energy equation Adsorption is a spontaneous process so ∆G is negative. At equilibrium it becomes zero and ∆H = T∆S is attained.
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Directions: In the following questions, A statement of Assertion (A) ...
Assertion (A): At the equilibrium position in the process of adsorption ∆H = T∆S.
Reason (R): Adsorption is accompanied by decrease in surface energy.
Explanation:
Equilibrium in Adsorption:
Adsorption is a process in which atoms, ions, or molecules from a gaseous or liquid phase adhere to a surface. At the equilibrium position in the process of adsorption, the rate of adsorption becomes equal to the rate of desorption. This means that the amount of adsorbate molecules on the surface remains constant over time.
Entropy Change (∆S):
Entropy is a measure of the randomness or disorder of a system. In the process of adsorption, the adsorbate molecules become more ordered and confined to the surface, resulting in a decrease in entropy. Therefore, the entropy change (∆S) for adsorption is negative.
Enthalpy Change (∆H):
Enthalpy is a measure of the heat energy absorbed or released during a chemical process. In the case of adsorption, the enthalpy change (∆H) at the equilibrium position is related to the temperature (∆T) and the entropy change (∆S) as follows:
∆H = T∆S
This equation is known as the Gibbs-Helmholtz equation and describes the relationship between the enthalpy change and the entropy change at equilibrium.
Decrease in Surface Energy:
Adsorption is accompanied by a decrease in surface energy. When adsorbate molecules adhere to the surface, they reduce the total area of the surface available for interaction with the surrounding medium. This reduction in surface area leads to a decrease in the surface energy of the system.
Explanation of Assertion and Reason:
The assertion (A) states that at the equilibrium position in the process of adsorption, ∆H = T∆S. This is true because it follows from the Gibbs-Helmholtz equation, which relates the enthalpy change (∆H) to the temperature (∆T) and the entropy change (∆S).
The reason (R) states that adsorption is accompanied by a decrease in surface energy. This is also true because when adsorbate molecules adhere to the surface, they reduce the total surface area, leading to a decrease in surface energy.
Conclusion:
Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is option B. Both A and R are true, and R is the correct explanation of A.