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Calculating work for winter 2013 midterm 4.B.

Posted: Wed Feb 14, 2018 1:28 pm
by Christina Cen 2J
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?

Re: Calculating work for winter 2013 midterm 4.B.

Posted: Wed Feb 14, 2018 1:35 pm
by Swetha Sundaram 1E
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)

Re: Calculating work for winter 2013 midterm 4.B.

Posted: Wed Feb 14, 2018 1:36 pm
by Swetha Sundaram 1E
we can't use the regular w=-p*deltaV is the irreversible equation, also the pressure isn't constant from point b to c

Re: Calculating work for winter 2013 midterm 4.B.

Posted: Wed Feb 14, 2018 1:54 pm
by Christina Cen 2J
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?

Re: Calculating work for winter 2013 midterm 4.B.

Posted: Thu Feb 15, 2018 3:11 pm
by Lorie Seuylemezian-2K
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