My question is: when oil and water from separate containers are poured into the same container and given time to equilibrate, is the entropy change positive, negative, or zero? I've been told that there is zero change in entropy because the water and oil do not mix at all. However, I suspect that there is a negative entropy change due to oil-water interactions at the oil-water interface. There will be interface tension (surface tension) in both the oil and water since the molecules at the interface because both species experience much greater cohesive forces than adhesive forces, but isn't it inevitable that there will be interactions between some small fraction of the billions of water and oil molecules at the interface? If there was some interaction, wouldn't this cause a negative change in entropy since water forms clathrate structures around hydrophobic regions of molecules? So just to be clear, I'm asking: 1. What is the change in entropy when mixing oil and water after letting the system equilibrate? 2. Are there interactions between oil and water molecules at the oil-water interface? 3. If there are interactions, do they affect the entropy of the system? Also, I'm new to physicsforums.com and I'm not totally sure of how to follow the template for posting an assignment that is totally theoretical and does not involve equations. I think I followed it for the most part, but I'm open to criticism! Thanks!