If I have a solution of salt or sugar dissolved in water, the solute will never settle out or "fall to the bottom", no matter low long I wait. Why is that?
Since salt and sugar (in their pure, solid forms) are denser than water, I would intuitively expect that gravity would eventually pull all the salt and sugar to the bottom. Why doesn't this happen?
Now, I'm guessing that salt and sugar solutions have lower energy than mixtures of solid salt or solid sugar with water. So that may explain why salt and sugar don't spontaneously settle out; reactions tend to proceed from a high-energy state to a lower-energy state, not vice versa. (In "explain like I'm 5" terminology, maybe sugar sticks to water better than sugar sticks to sugar.) Is that accurate?
I've heard that the favorability of a reaction is determined by such things as energy, entropy and enthalpy, but I don't know the details. I'm guessing the answer has something to do with those.
This question is inspired by this question over at the Earth Science site: Why does the salt in the oceans not sink to the bottom?
(I'm surprised that I wasn't able to find a previous question about why solutions don't settle. All I found was a question about why colloids don't settle, which is also an interesting question, but it's not the same thing.)