Question

Surfactant molecules can cluster together as micelles, which are colliod sized cluster of molecules. Micelles form only above critical micelle concentration (CMC) and above certain temperature called Kraft temperature. $\Delta H$ of micelle formation can be positive or negative. Which of the following is NOT TRUE about micelle formation?

• A. $\Delta S$ of micelle formation is positive
• B. The hydrophobic part lie towards interior of micelle
• C. The hydrophillic part lie towards surface of micelle
• D. $\Delta S$ of micelle formation is negative

Answer 1

The correct option is D $\Delta S$ of micelle formation is negative

The micelle formation releases water molecules which solvates the hydrophillic head groups. The release of water greatly increase the entropy.

The formation of micelle only above certain tempertaure called Kraft temperature suggests positive $\Delta S$ of micelle formation which even overcome effect of positive $\Delta H$ micelle formation. Besides, kinetic effect also become important at high temperature.