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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: bu2012 on September 20, 2011, 02:47:59 PM

Title: Ideal monatomic gas: final temp
Post by: bu2012 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?
Title: Re: Ideal monatomic gas: final temp
Post by: Enthalpy 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.
Title: Re: Ideal monatomic gas: final temp
Post by: SABRY 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.