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Degrees of freedom affect on heat capacity ratio

  1. Sep 29, 2009 #1
    1. The problem statement, all variables and given/known data

    Why would vibrational and rotational degrees of freedom affect the heat capacity ratio more for N2 and CO2 than He or Ar? Would this occur at room temperatures?

    2. Relevant equations

    d.o.f.: 3N
    vibrational d.o.f., linear molecule: 3N - 5
    nonlinear: 3N - 6

    3. The attempt at a solution

    My book says that the vibrational d.o.f. will be more active for heavier molecules. Why is this? Does this mean there would be a larger change from the expected heat capacity ratio as predicted by the equipartition theorem? I don't understand whether it would negatively or positively affect it, or why. Also, I thought it was only an issue for REALLY high temperatures, not room temperature. A little clarification would be helpful.
  2. jcsd
  3. Sep 30, 2009 #2


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    Helium and argon are monatomic. They do not have vibrational or rotational degrees of freedom. All they can do when you add energy to them is move faster, i.e. partition the energy among the three translational degrees of freedom.
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