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Question about intermolecular forces in gases

  1. Nov 10, 2008 #1
    Hi, my question is this. Is a gas with a positive intermolecular potential like a gravity potential in a pendulum???? By this I mean if you compress and the expand the gas the force goes from max potential to a minimum ,creating molecular acceleration in the process and then reverses the process with expansion , correct??? PE <=> acceleration.
    As I understand it this is similar to a pendulum, Grav P <=> acceleration.
    Disregarding the small heat loss,,, isnt it true that the total energy of this reciprocal transformation is constant through the whole cycle in a pendulum?????
    Is this true with the potential in the gas ??? Disregarding the kinetic energy added through the action of compression and the original kinetic energy,,,the PE <=> Kinetic energy total is constant throughout the process????

    Any insight into this question would be apprecciated Thanks
  2. jcsd
  3. Nov 10, 2008 #2


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    See Joule-Thomson expansion/effect, and Joule-Thomson inversion temperature.
  4. Nov 11, 2008 #3
    Thanks Bystander I should have specified a gas under the inversion temp.
    Actually this whole question came from trying to understand the workings of the Linde J-T throttle oxygen cooling system.
    IN cooling a volume of oxygen from ambient to liquid temp thru repeated cycles it seemed like a large amount of kinetic energy had to be conducted out of the system.
    I think I understand the reduction of temperature through increased potential due to expansion but dont see how any energy could actually leave the system in that phase.

    The only way it seemed to make sense was if compression exploited the force in the reverse direction allowing more energy to leave the system via the cooling interface in the high pressure phase of the cycle. But in my reading I never found this discussed , only reference to cooling by expansion. Excuse me if I am missing something fundemental this whole area is somewhat new to me.
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