Question:
Which of the following statements is true for adsorption?
Which of the following statements is true for adsorption?
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To remember the difference easily: ADsorption is a Surface phenomenon (think of "Adding onto a table"), while ABsorption is a Bulk phenomenon (think of a sponge swallowing water into its entire volume)!
Updated On: Jun 12, 2026
- It is accompanied by evolution of heat.
- It is a bulk phenomenon.
- It is independent of surface area.
- It is independent of temperature.
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Question:
The question asks us to identify the correct statement regarding the thermodynamic and physical characteristics of the adsorption process.
Step 2: Key Formula or Approach:
Adsorption is the accumulation of molecular species at the surface rather than in the bulk of a solid or liquid. Thermodynamically, when gas or solute particles adhere to a solid surface, residual surface forces decrease, causing a release of surface energy. Thus, adsorption is spontaneously exothermic ($\Delta H < 0$).
Step 3: Detailed Explanation:
Let us evaluate each statement to see why it stands or fails:
(A) It is accompanied by evolution of heat: True. Because new attractive interactions are formed between the adsorbate molecules and the adsorbent surface, energy is invariably released. Hence, $\Delta H$ is negative (exothermic process).
(B) It is a bulk phenomenon: False. Adsorption happens strictly at the boundary interface or surface layer. It is absorption that represents a bulk phenomenon where substance permeates uniformly throughout the mass.
(C) It is independent of surface area: False. Since it is a surface-bound event, increasing the total accessible surface area (e.g., using finely divided or porous solids) directly scales up the total amount of material adsorbed.
(D) It is independent of temperature: False. According to Le Chatelier's principle, because physical adsorption is exothermic, an increase in temperature shifts the equilibrium backward, decreasing the extent of adsorption.
Therefore, statement (A) is the only true description.
Step 4: Final Answer:
The true statement for adsorption is that it is accompanied by the evolution of heat, which corresponds to option (A).
The question asks us to identify the correct statement regarding the thermodynamic and physical characteristics of the adsorption process.
Step 2: Key Formula or Approach:
Adsorption is the accumulation of molecular species at the surface rather than in the bulk of a solid or liquid. Thermodynamically, when gas or solute particles adhere to a solid surface, residual surface forces decrease, causing a release of surface energy. Thus, adsorption is spontaneously exothermic ($\Delta H < 0$).
Step 3: Detailed Explanation:
Let us evaluate each statement to see why it stands or fails:
(A) It is accompanied by evolution of heat: True. Because new attractive interactions are formed between the adsorbate molecules and the adsorbent surface, energy is invariably released. Hence, $\Delta H$ is negative (exothermic process).
(B) It is a bulk phenomenon: False. Adsorption happens strictly at the boundary interface or surface layer. It is absorption that represents a bulk phenomenon where substance permeates uniformly throughout the mass.
(C) It is independent of surface area: False. Since it is a surface-bound event, increasing the total accessible surface area (e.g., using finely divided or porous solids) directly scales up the total amount of material adsorbed.
(D) It is independent of temperature: False. According to Le Chatelier's principle, because physical adsorption is exothermic, an increase in temperature shifts the equilibrium backward, decreasing the extent of adsorption.
Therefore, statement (A) is the only true description.
Step 4: Final Answer:
The true statement for adsorption is that it is accompanied by the evolution of heat, which corresponds to option (A).
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