Tuesday, July 20, 2010

Pig Smackdown: Entropy of Oil and Water

Commenters took the pig to task for his criticism of Sean Carroll's analysis. I still think that he is misleading in saying that water and oil attract - true enough in some absolute sense, but when they are mixed they effectively repel each other. He is at least mostly right about the entropy though. The effective repulsion of the oil and water forces water molecules to surround the droplets of oil with highly ordered two dimensional structures to form clathrates. The two D water is much more orderly that three D water, so minimizing their area (the area of interface between oil and water) maximizes the entropy.

See eg: garrettgrisham and also Arun's link in the comments.

jpd also has a point, also covered in the gg link. It's the overall entropy of the universe that counts here, but that's hard to keep track of sometimes, so look at the Gibbs free energy (G=H-TV in my notation).

See also Wikipedia: Gibbs free energy