Calculate the heat capacity ratio for a diatomic ideal gas.(adsbygoogle = window.adsbygoogle || []).push({});

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Using the equipartition theorem, I calculate:

Cp / Cv = (Cv + R) / Cv = (7/2 R + R) / (7/2 R) = (9/2 R) / (7/2 R) = 9/7 ~ 1.286

According to the equipartition theorem, I assign each vibrational degree of freedom 1 R and the translational and rotational degrees of freedom are 1/2 R. A diatomic ideal gas has 3(2) = 6 d.o.f. with 3 translational, 2 rotational, 1 vibrational.

However, here the vibrational d.o.f. are not considered separately - and in the first link it shows that the experimental results are actually closer to 1.4 (which you would predict if the vibrational d.o.f. were assigned the same values as the other two). What's going on?

http://en.wikipedia.org/wiki/Heat_capacity_ratio

http://en.wikipedia.org/wiki/Adiabatic_process#Ideal_gas_.28reversible_case.29

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# Homework Help: Heat capacity ratio for diatomic gases

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