Physics Asked on December 29, 2021
I studied a sciences of climate change module with the OU a while ago, I’m half remembering something that’s bugging me and wonder whether any could help provide some clarification?
I remember that an increase in degrees of freedom of a molecule are related to increase internal energy / heating. Hence this was the reason that gases such as CO2 were contributing more to global heating than diatomic Nitrogen or Oxygen.
In addition when we look at very high global warming potential GWP gases such as refrigerant R22 CFCs we see these are very long chained molecules whit a higher number of degrees of freedom. Hence these gases absorb more solar radiation and exasperate the global heating problem? (ability to store energy was presumably why R22 was selected as a good refrigerant).
Is this thinking right?
Also, does anyone know / can someone confirm?
Degrees of freedom of Diatomic Nitrogen?
Degrees of freedom of Diatomic Oxygen?
Degrees of freedom of Carbon Dioxide?
Thanks
PF
The increasing in degrees of freedom are related to an increase of the heat capacity ratio $$gamma = frac{c_P}{c_V},$$ but not necessarily with an increase in the internal energy of the molecule. The CO2 acts as a greenhouse effect gas because it's much more efficient than NO2 and O2 at absorbing infrarred (IR) radiation:
About the CFCs, I'm not really sure, but I'd assume they are also good IR absorbers, although their main problem is destroying the ozone layer, but that's a different topic.
Regarding degrees of freedom (DoF), you can understand them as different kinds of motion a molecule can have:
Pd: vibrations should be included as well, but it's very difficult to make a molecule vibrate, so it's often left aside.
Answered by Pablo Lemos on December 29, 2021
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