Calculating work for winter 2013 midterm 4.B.


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Christina Cen 2J
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Calculating work for winter 2013 midterm 4.B.

Postby Christina Cen 2J » Wed Feb 14, 2018 1:28 pm

Going for point B to point C has a change in both pressure and volume, but the answer seems to only account for the work done based on the change in pressure. Yet it states both equations. Why do we not calculate the work done by change in volume?

Swetha Sundaram 1E
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Re: Calculating work for winter 2013 midterm 4.B.

Postby Swetha Sundaram 1E » Wed Feb 14, 2018 1:35 pm

Going from point B to point C, we are told that it is a reversible reaction so we use the equation that is w--nRTln(V2/V1)

Swetha Sundaram 1E
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Re: Calculating work for winter 2013 midterm 4.B.

Postby Swetha Sundaram 1E » Wed Feb 14, 2018 1:36 pm

we can't use the regular w=-p*deltaV is the irreversible equation, also the pressure isn't constant from point b to c

Christina Cen 2J
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Re: Calculating work for winter 2013 midterm 4.B.

Postby Christina Cen 2J » Wed Feb 14, 2018 1:54 pm

But it uses w = -nRTln(P1/P2), not -nRTln(V1/V2). Shouldn't we use both equations since there is both a change in pressure and volume?

Lorie Seuylemezian-2K
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Re: Calculating work for winter 2013 midterm 4.B.

Postby Lorie Seuylemezian-2K » Thu Feb 15, 2018 3:11 pm

What equation we use is based on if the equation is reversible or not. If it is reversible we use the equation with R in it and if it is irreversible we use the equation with w=-pextdeltaV


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