Winter 2013 Midterm: Question #4


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megan_thi_2j
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Joined: Wed Sep 21, 2016 2:55 pm

Winter 2013 Midterm: Question #4

Postby megan_thi_2j » Sun Feb 12, 2017 6:55 pm

For part A of this question, it asks to calculate the work for each step:
A to B
B to C
C to A
Can someone clear up why for B to C, we use the reversible work formula, while for C to A, we use the irreversible work formula?
I can't seem to picture visually from the graph why one is reversible and one is not reversible

Thanks!

Rika Jitosho 2E
Posts: 29
Joined: Fri Jun 17, 2016 11:28 am

Re: Winter 2013 Midterm: Question #4

Postby Rika Jitosho 2E » Mon Feb 13, 2017 1:12 am

For B to C, by looking at the y-axis of the graph, the pressure decreases, so in other words, pressure is not constant. We know from class that under irreversible conditions, pressure is constant, but since that is not the case, we have to use the work equation for variable pressure (reversible work formula). By this logic, we can see from C to A that pressure remains the same, so in this case we would use the work equation for constant pressure (irreversible work formula).

204751840 2E
Posts: 19
Joined: Tue Oct 04, 2016 3:00 am

Re: Winter 2013 Midterm: Question #4

Postby 204751840 2E » Wed Feb 15, 2017 12:13 am

Just to clarify, if the pressure changes, but the volume does not, no work is done, right?

Emily Wang 1H
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Joined: Sat Jul 09, 2016 3:00 am
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Re: Winter 2013 Midterm: Question #4

Postby Emily Wang 1H » Wed Feb 15, 2017 8:19 am

Yes, if there is no change in volume, then there is no work done by expansion because delta V will be 0.


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