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At room temperature....

How long will the sugar stay suspended once dissolved ?

What governs the rate of settling ?

What part does Brownian motion play ?

Sugar might be a bad example...please substitute as needed.

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Anything dissolved is kept "suspended" by brownian motion. Theoreticly there will be a small gradient of concentration due to gravity, but this is unmeasurable for sugar. (Barometric formula). For much bigger particles (ãbout µm) , this gradient can be determined.

The sugar will stay dissolved until the water evaporates, then the sugar will form a solid residue. (if You are lucky, as crystals) Settling does not occur with molecules.

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  • $\begingroup$ I'd like to see an explicit mention of entropy vs internal energy, and a bit more thermodynamics in the answer, rather than just a microscopically detailed mechanical description. $\endgroup$
    – genneth
    Feb 21, 2011 at 10:14
  • $\begingroup$ @ genneth, Feel free to write an answer including entropy. $\endgroup$
    – Georg
    Feb 21, 2011 at 11:02

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