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Change in entropy at constant temperature 
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#1
Nov2109, 12:00 PM

P: 14

1. The problem statement, all variables and given/known data
Calculate the entropy change when 0.011m3 of a perfect gas at a constant temperature of 273K is compressed from an initial pressure 1x10^5 N/m/m to a pressure of 1x10^6 N/m/m. I know the equation but cannot work out Q!! Please help! 2. Relevant equations dS=Q/T 3. The attempt at a solution 


#2
Nov2109, 12:57 PM

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PF Gold
P: 2,532

Hi ricof, welcome to PF. Can you combine the First Law with what you know about the energy of an ideal gas at constant temperature?



#3
Nov2109, 02:21 PM

P: 29

Some more relevant equations.
The first law [tex]\Delta E=Q+W[/tex] Work for isothermal expansion [tex]W=nRTln\frac{V_{f}}{V_{i}}[/tex] If you combine this with what you know about change in internal energy at constant temperature, like Mapes said, and that integral of yours, you can figure out the answer. 


#4
Nov2109, 03:48 PM

P: 14

Change in entropy at constant temperature
Because T is constant, there is no change in internal energy right?
And also, in the above equation for isothermal expansion, how is n calculated? 


#5
Nov2109, 05:27 PM

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PF Gold
P: 2,532




#6
Nov2109, 08:08 PM

P: 14

Ok, so as dE = 0,
Q = W and as PV = nRT, W=PV ln (v1/v2) which is Q Thanks guys, my answer is correct. Thanks for helping! 


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