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Topic: Ideal monatomic gas: final temp  (Read 2696 times)

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Offline bu2012

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Ideal monatomic gas: final temp
« on: September 20, 2011, 02:47:59 PM »
I am to expand adiabtically and reversibly from 22.7 L/mol and 1.00 bar to a molar volume of 45.4 L/mol. I am to find the final pressure and final temperature. I think that I have the final pressure one by using V2/V1 = (T1/T2)Cv/R and just substituting PV/R for the T's. However, I am not sure how I find the final temperature. Do I use the same equation or a different one?

Offline Enthalpy

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Re: Ideal monatomic gas: final temp
« Reply #1 on: October 10, 2011, 04:30:37 PM »
Nearly the same formula, with P/P instead of V/V, and Cp instead of Cv. Re-think each time if P2 shall be greater or smaller than P1.

And remember that gases may not be perfect, especially if density gets close to a liquid, or if they approach a boiling temperature... As well, Cv may (and does) vary over temperature.

Offline SABRY

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Re: Ideal monatomic gas: final temp
« Reply #2 on: October 12, 2011, 10:42:16 PM »
1. For adiabatic expansion use the equation PVk = constant where k is the ratio of specific heat Cp/Cv.

2. From the above equation, P2 can be determined.

3. The above equation coupled with the universal gas law PV = nzRT, we can arrive at following equation:

T2 = T1(P2/P1)m

Where m = (k-1)/K

4. Knowing P2, T2 can be determined from the above equation

5. P & T are in absolute units.

6. Include Z the compressibility factor to be more accurate.

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