JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Surface Chemistry

Micelle formation is governed by the hydrophobic effect. While the surfactant stays dispersed as single ions, the water around each hydrocarbon tail is forced into an ordered, cage-like structure; as the tails gather into a micelle this structured water is freed back into the bulk, and the resulting rise in disorder makes the entropy change positive. The aggregation itself has to break those favourable water structures and returns little compensating bond energy, so the enthalpy change is positive and the process is endothermic. It is driven not by heat released but by the large positive entropy term, so the correct statements are that micelle formation is endothermic and that its entropy change is positive.