Question

Surfacants are molecules with a hydrophillic head group (maybe charged and a hydrophobic (nonpolar) tail. Individually, the hydrophillic head group of a surfactant could interact with water molecules through intermolecular forces and thus decrease the surface tension compared to pure water. At a certain concentration, surfactants in water can aggregate spontaneously to form micelles which has the hydrophillic head groups pointing out towards the water and the nonpolar tails are kept inward toward the micelle center.

Explain in 3 sentences or less, why the spontaneous formation of micelles does not vioalate the second law of thermodynamics.

Answer 1

When surfactants are free the water molecules have less degrees of freedom due to their arrangement around the hydrophilic head group. When the micelle is formed, the water molecules are no longer directly bound to individual molecules which increases their degrees of freedom and the entropy of the system. As in micelle formation no bond breaking or formation occurs, no entropy change happens due to which the entropy increase from water does not violate but support second law of thermodynamics.