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Determination of intermolecular forces using surface tension

  1. Dec 7, 2012 #1
    Hi there. I have found the surface tension for liquid etanol on a given problem. Then the problem says: supposing that the coordination number for etanol is 12, what value does the intermolecular interaction energy has?



    I have ##\gamma=21,26355\frac{dyna}{cm}##, gamma is the surface tension that I've found.

    The coordination number gives the number of molecules around one molecule in the liquid. I think that because the surface tension happens in the interface, the coordination number in there is 12/2=6.

    I also know that ##\gamma=F/2l##, I have this in my notes from class. This is what you get by analysing the virtual work by pushing a thin film a ##\Delta x## distance.

    ##F\Delta x=2l\Delta x \gamma##

    PS: I made a mistake in the title, it's not the determination of intermolecular forces, but intermolecular energy.
     
    Last edited: Dec 7, 2012
  2. jcsd
  3. Dec 7, 2012 #2

    haruspex

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    A quick Google on the subject suggests it will be more than half. I see a couple of places where a bulk number of 6 is presumed to correspond to a surface number of 5. But I couldn't find a general rule or any theoretical basis for the assumption. With optimally stacked spheres, each interior sphere has 12 neighbours, while each on a flat surface would have 9.
     
  4. Dec 7, 2012 #3
    Thanks for your answer. Do you have any idea on how to determine the interaction energy using the surface tension and the coordination number?
     
  5. Dec 7, 2012 #4

    haruspex

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    It's a field I know nothing about, but see if this helps: http://mail.vssd.nl/hlf/d007ch02.pdf
     
  6. Dec 7, 2012 #5
    Thank you very much. I think it will help.

    I would need to know how to determinate systematically the coordination number for molecules in the surface. And I would like to know also how to derive the equations (2.4) to (2.8).
     
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