Q.41 Given below are two statements. One is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: The second law of thermodynamics states that the total entropy of a system plus that of its
surroundings always increases.
Reason R: The release of water from nonpolar surfaces responsible for the hydrophobic effect is favourable
because water molecules free in solution are more disordered than they are when they are associated with
nonpolar surfaces.
In the light of above, choose the correct answer from the options given below:
1. Both A and R are correct and R is the correct explanation of A
2. Both A and R correct but R is not the correct explanation of A
3. A is correct but R is incorrect
4. A is correct but R is incorrect
Second Law Thermodynamics Assertion-Reason: Entropy & Hydrophobic Effect
The second law states entropy of system plus surroundings increases for spontaneous processes, while the hydrophobic effect drives water disorder increase. Both A and R are correct, but R exemplifies rather than explains A directly; correct answer is option 2.
Correct Answer
Option 2: Both A and R correct but R is not the correct explanation of A.
Assertion A accurately states the second law: for spontaneous processes, ΔS_universe = ΔS_system + ΔS_surroundings > 0. Reason R describes the hydrophobic effect where releasing ordered water cages around nonpolar groups increases solvent entropy, driving folding.
Option Analysis
Option 1: Both Correct and R Explains A
Incorrect—R illustrates entropy increase (water disorder) as a consequence of the second law, not its cause or general explanation. The law applies universally beyond hydrophobicity.
Option 2: Both Correct but R Not Explanation (Correct)
A is the fundamental principle; R is a biochemical example where hydrophobic collapse is entropically favorable (ΔS_water > 0 compensates ΔS_protein < 0). No direct explanatory link.
Option 3: A Correct, R Incorrect
Wrong—R correctly describes hydrophobic solvation: water forms low-entropy clathrate structures around hydrophobes, release yields higher bulk entropy.
Option 4: A Correct, R Incorrect
Duplicate invalid option; R is factually accurate per hydrophobic thermodynamics.
| Option | Evaluation | Correct? | Reason |
|---|---|---|---|
| 1 | R explains A | No | Example ≠ general law |
| 2 | Both correct, no explanation | Yes | Hydrophobicity exemplifies |
| 3 | R incorrect | No | Water disorder fact |
| 4 | R incorrect | No | Duplicate invalid |
Exam Strategy
Assertion-Reason tests if R causally derives A vs. merely relates. Hydrophobic effect entropy aligns with but doesn’t define second law universality.
