[Camlost]

Hello,

I have a question about hydrophobic interactions, or more specifically, micelles forming from lipids in water. I'm aware that the entropy in a solution in which micelles are forming increases, and it is thus an exothermic, spontaneous reaction. I don't, however, understand the logic of the entropy actually increasing as the molecules in the solution actually becomes MORE ordered in the forming of micelles. Is there a temperature increase or something else to account for the increase in entropy? Because as far as I know, the actual ordering of molecules should decrease the entropy.

What particularly confuses me, is that my biochemistry book, my chemistry lecturer and wikipedia seems to be contradicting eacother. Here's what my biochem book says:
"Micelles - All hydrophobic groups are sequestered from water; ordered shell of H2O molecules is minimized, and entropy is further increased."(Lehninger, Principles of Biochemistry, 4th ed.)

And here's what wikipedia and my lecturer says:
"Micelles only form when the concentration of surfactant is greater than the critical micelle concentration (CMC), and the temperature of the system is greater than the critical micelle temperature, or Krafft temperature. The formation of micelles can be understood using thermodynamics: micelles can form spontaneously because of a balance between entropy and enthalpy. In water, the hydrophobic effect is the driving force for micelle formation, despite the fact that assembling surfactant molecules together reduces their entropy."

This last part confuses me greatly. "...despite the fact that assembling surfactant molecules together reduces their entropy". What exactly happens? The molecules gets more ordered as stated here specifically, and the entropy is reduced, but the overall entropy increases? HOW?! Someone kindly enlighten me. Oh, if someone could actually use dG=dH - TdS and just insert the numbers and show me why things are the way they are, that'd probably be a help as well.

[Borek]

The molecules gets more ordered as stated here specifically, and the entropy is reduced, but the overall entropy increases?

Molecules that get ordered are not all taking part in the process. Ordering is most likely exothermic.