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Why the process of diffusion takes place

  1. Mar 14, 2007 #1
    I wonder why the process of diffusion takes place...
    Why should the molecules of gas for example, travel from a region of higher concentration to the region of lower concentration till an equilibrium is achieved?

    I'll be thankful for your guidance :)
  2. jcsd
  3. Mar 14, 2007 #2


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    Basically, it's just entropy in action. Assuming gases of similar density, the least-ordered state is preferred since it requires the least energy expenditure to maintain.
  4. Mar 15, 2007 #3
    Like danger said , a lower concentration of molecules versus a higher concentration of molecules , the lower concentration is the "more orderly system" and less energy would be required to remain in that state. The molecules would prefer to move to that area . The movement itself is due to the constant movement of gas particles.
  5. Mar 15, 2007 #4

    Claude Bile

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    The higher the concentration of molecules, the more likely it is for a given molecule to suffer a collision traveling over a given distance. This means that when a molecule gets knocked toward regions of higher pressure (concentration), it travels, on average a shorter distance before it collides with another particles than when it gets knocked toward a region of lower pressure (We call this concept the mean free-path).

    This means that molecules are more likely to drift to regions of low pressure over time. The fact that there is a great many molecules, means that you will get a net drift of molecules from the high pressure region to the low pressure region.

    Keep in mind that diffusion is inherently a statistical phenomenon - the vast numbers of particles involved means that the behaviour of the group can be predicted with accuracy despite this.

  6. Mar 15, 2007 #5


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    Staff: Mentor

    Momentum and energy.
  7. Mar 16, 2007 #6
    May i explain this way (not concerning entropy) : Suppose there's a reservoir full of water and a mall drop of ink inside it. For brownian motion, an individual molecule, both water and ink, will move to an unpredictable spot within the reservoir after some time. The probability of finding a given molecule after a long enough period of time is equal everywhere in the reservoir. And thus the diffusion has taken place.
    The time to get to equilibrium depends on many things namely: temperature (brownian motion), reservoir shape etc..
  8. Mar 19, 2007 #7
    Thanks from everyone contributing to this thread...
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