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Entropy and osmosis

  1. Aug 13, 2009 #1
    what exactly browian motion and osmosis does to the second law of motion? nothing right? because anyway one will set an experiment trying to locate semipermeable membrane, he\she already exert more energy.

    (i need you to verify me)
  2. jcsd
  3. Aug 13, 2009 #2


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    Diffusion of a substance from an area of high concentration to an area of lower concentration will increase the entropy of the system.

    Brownian motion is tricky to talk about in terms of entropy. Brownian motion (the random walk of particles) is something that occurs with single particles. Entropy, a thermodynamic concept, applies to large ensembles of particles, not single particles. Of course, the Brownian motion of large ensembles of particles is diffusion.
  4. Aug 13, 2009 #3
    I think you need to also consider thermo-osmosis. Or that, in a permeable membrane which has some sort of an entropy/temperature gradient, particles will always diffuse towards higher entropy since it is thermodynamically favored.
  5. Aug 13, 2009 #4
    well it is a difussion if the membrane got holes alowing only small objects move both sides and big stay in one side. you build a pressure, when you remove the membrane there is energy, and that is not just a few particles but a large quantity of microscopic particles
  6. Aug 13, 2009 #5
    and Maxwell was right, there can be a demon, even if it is in a small case
  7. Aug 13, 2009 #6
    The membrane is just a lever for converting the osmotic potential energy (that you prepared) into gravitational potential energy (which you know how to harness). You can tell that it isn't creating energy by the fact that, unlike Maxwell's demon, the operation of your device can't repeat in a closed cycle (you have to perform more work to separate back the solutes first).
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