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-   -   PV Diagram of a monoatomic gas and diatomic gas (http://www.physicsforums.com/showthread.php?t=559996)

 Zenderson3 Dec13-11 10:01 PM

PV Diagram of a monoatomic gas and diatomic gas

I'm reviewing a question on a previous test but am having trouble finding the solution for it.

We were told to draw a PV diagram of a monoatomic ideal gas that undergoes an isothermal compression from Va to Vb and then is allowed to expand adiabatically and quasistatically back to Va again.

I was able to comprehend this portion of the question fine but then got stuck on the next part that asked how this sketch would look if the molecule was diatomic. Aside from the difference in internal energy due to the degrees of freedom of a diatomic molecule I can't seem to find any other major implications of a monoatomic gas vs. a diatomic gas. Furthermore I can't seem to figure out how the internal energy of the system would tie into this diagram.

 Andrew Mason Dec14-11 12:03 AM

Re: PV Diagram of a monoatomic gas and diatomic gas

Quote:
 Quote by Zenderson3 (Post 3667525) I'm reviewing a question on a previous test but am having trouble finding the solution for it. We were told to draw a PV diagram of a monoatomic ideal gas that undergoes an isothermal compression from Va to Vb and then is allowed to expand adiabatically and quasistatically back to Va again. I was able to comprehend this portion of the question fine but then got stuck on the next part that asked how this sketch would look if the molecule was diatomic. Aside from the difference in internal energy due to the degrees of freedom of a diatomic molecule I can't seem to find any other major implications of a monoatomic gas vs. a diatomic gas. Furthermore I can't seem to figure out how the internal energy of the system would tie into this diagram.
The same work is done on or by the gases during the compression and expansion parts. But their heat capacities are different. So their changes in internal energies in the isothermal compression part will be different which means that their final internal energies will differ.

The adiabatic condition: $PV^\gamma = K$ applies during the adiabatic expansion. Use this to determine how the adiabatic expansion path for the diatomic gas will compare to that of the monatomic gas.

AM

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