Question:
Which of the following statements is NOT True with respect to physisorption?
Which of the following statements is NOT True with respect to physisorption?
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Adsorption restricts the freedom of motion of gas molecules, so entropy decreases.
Updated On: Nov 12, 2026
- It is reversible
- It is multimolecular.
- \(\Delta H\lt 0\)
- \(\Delta S>0\)
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept
Physisorption is physical adsorption by weak van der Waals forces. It is reversible, multilayered and exothermic.
Step 2: Check the thermodynamics
Adsorption is spontaneous, so \(\Delta G\lt 0\). Adsorbed molecules lose freedom of motion, so \(\Delta S\lt 0\). Then \(\Delta H=\Delta G+T\Delta S\lt 0\).
Step 3: Compare the options
Reversible, multimolecular and \(\Delta H\lt 0\) are all true for physisorption. The statement \(\Delta S>0\) is false.
Final Answer:
The statement that is not true is that the entropy change is positive. \[ \boxed{\text{(D) }\Delta S>0} \]
Physisorption is physical adsorption by weak van der Waals forces. It is reversible, multilayered and exothermic.
Step 2: Check the thermodynamics
Adsorption is spontaneous, so \(\Delta G\lt 0\). Adsorbed molecules lose freedom of motion, so \(\Delta S\lt 0\). Then \(\Delta H=\Delta G+T\Delta S\lt 0\).
Step 3: Compare the options
Reversible, multimolecular and \(\Delta H\lt 0\) are all true for physisorption. The statement \(\Delta S>0\) is false.
Final Answer:
The statement that is not true is that the entropy change is positive. \[ \boxed{\text{(D) }\Delta S>0} \]
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