Question

The number of incorrect statement/s from the following is/are ____
A. Water vapours are adsorbed by anhydrous calcium chloride.
B. There is a decrease in surface energy during adsorption.
C. As the adsorption proceeds, $\Delta H$ becomes more and more negative.
D. Adsorption is accompanied by decrease in entropy of the system.

Answer 1

Correct Answer: 2

The task is to determine the number of incorrect statements among the provided options: A, B, C, and D.

1. Statement A: "Water vapours are adsorbed by anhydrous calcium chloride." This statement is incorrect. Anhydrous calcium chloride is a desiccant and effectively adsorbs water vapours due to its hygroscopic nature.
2. Statement B: "There is a decrease in surface energy during adsorption." This statement is correct. During adsorption, particles attract and adhere to the surface, reducing the surface energy since the resulting system is more stable.
3. Statement C: "As the adsorption proceeds, ΔH becomes more and more negative." This statement is incorrect. The enthalpy change (ΔH) for adsorption is typically negative initially, but as adsorption sites become saturated, |ΔH| decreases (i.e., becomes less negative) because fewer and less favorable sites are left.
4. Statement D: "Adsorption is accompanied by decrease in entropy of the system." This statement is correct. Adsorption leads to a more ordered system since particles on the surface are less randomly oriented compared to gas or liquid state; thus, entropy decreases.