# DBT JRF 2022 — Question 8

Exam: DBT JRF 2022 · Section: A · Topic: Biochemistry › Thermodynamics & Hydrophobic Effect · Difficulty: Medium

## Question

The introduction of the nonpolar molecule (toluene) into water results in:

## Options

- **A.** a decrease in the entropy of water.
- **B.** an increase in the entropy of water.
- **C.** no change in entropy of water.
- **D.** modest exothermic dissolution.

## Answer

Option A

## Explanation

Hydrophobic effect and entropy of water: When a nonpolar molecule (e.g., toluene) is introduced into water, it cannot form hydrogen bonds with water. To maintain their hydrogen-bonding network, water molecules around the nonpolar solute organise into highly ordered 'clathrate' (cage-like) structures. • This increased ordering of water molecules DECREASES the entropy of water ( $\Delta S_{\text{water}} < 0$ ). • This entropy decrease is thermodynamically unfavourable and is the primary reason nonpolar molecules have low water solubility. • The process is endothermic in terms of entropy change — not exothermic dissolution. • The 'hydrophobic effect' that drives protein folding and membrane formation is primarily entropy-driven: burying hydrophobic groups releases ordered water, INCREASING entropy. Answer: Decrease in entropy of water (Option 1).

Source: https://mypyqbuddy.com/questions/the-introduction-of-the-nonpolar-molecule-toluene-into-6a104cd5920734408bc0c6e5