Help with Self Test 9.5A


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Help with Self Test 9.5A

Postby Susanna » Tue Feb 09, 2016 1:34 pm

Calculate the change in entropy when the volume of 2.00 mol Ar(g) is decreased from 10.00 L to 5.00 L while the temperature decreases from 300 K to 100 K. Assume ideal behavior.

The answer is -38.9 J K^-1 but I got -57.34 J K^-1.
I followed the example above and first used delta S = nRlnV2/V1 and got -11.53 J K^-1 and then used delta S = CvlnT2/T1 and Cv=nCv,m and got -45.81 J K^-1. I then added both delta S' together and got -57.34, can someone tell me where I went wrong or if you approached the problem differently? Thanks.

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Re: Help with Self Test 9.5A

Postby Chem_Mod » Tue Feb 09, 2016 8:21 pm

Your value -11.53 J/K is correct. However, when you calculate for the nCvln(T2/T1) I actually get the value -27.4 J/K.
To calculate did you do ?

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