KCET · Chemistry · Surface Chemistry

During adsorption of a gas on a solid at low temperature

A \(\Delta G < 0, \Delta H < 0, \Delta S < 0\)
B \(\Delta G>0, \Delta H>0, \Delta S>0\)
C \(\Delta G < 0, \Delta H < 0, \Delta S>0\)
D \(\Delta G < 0, \Delta H>0, \Delta S < 0\)

Verified Solution

Answer & Solution

Correct Answer

(A) \(\Delta G < 0, \Delta H < 0, \Delta S < 0\)

Step-by-step Solution

Detailed explanation

Adsorption is an exothermic process with \(\Delta H=\) negative and since, gas is being adsorbed to a solid the randomness of the gas is decreasing making \(\Delta S < 0\).
Also, \(\Delta G=\Delta H-T \Delta S\)
Here, \(T \Delta S\) is small negative value at low temperature and hence, \(\Delta G < 0\).
Which supports the spontaneity of the adsorption.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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