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GR9677 #79
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Comments |
shafatmubin
2009-11-04 15:17:49 | This link might help:
http://hyperphysics.phy-astr.gsu.edu/HBASE/hframe.html
It shows the variation of Cv of hydrogen gas with temperature. At very high temperatures, above 1000 K, there are 7 degrees of freedom because two additional degrees (apart from the 3 translational and 2 rotational degrees) become active. Can anyone explain what are these two new degrees of freedom? One of them is possibly vibrational, but what about the other?
hdcase
2009-11-04 21:46:12 |
Hyperphysics doesn't make this very clear, but wikipedia does:
http://en.wikipedia.org/wiki/Specific_heat_capacity#Diatomic_gas
The vibrational state (there is one degree of freedom from it, for a total of 6 degrees of freedom) adds R (instead of R/2) because it carries both a potential and kinetic term (both of which can "hold energy," which is essentially what the specific heat measures).
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shafatmubin
2009-11-05 13:12:22 |
Thanks hdcase. Vibrational energy contributing R instead of 2R makes things a lot more understandable.
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|  | petr1243
2008-03-18 11:45:15 | Roughly, Rotaional effects disappear below 25k, and all 3 effects will produce a specific heat of  at temperatures above 8000K. A good reference is ch.18 of the University Physics text. | | cyberdeathreaper
2007-02-03 15:05:37 | I found this equation helpful in solving the problem:
R)
Where
for linear molecules, and
for non-linear molecules.
I assumed that that
for very high temperatures. And of course, the rotational and vibrational contributions are 0 at very low temperatures, as Yosunism explained in the answer. | |
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