Midterm 2013 Q4A

[anatorres1B]

To calculate the work from B to C, it appears a variation of the work equation was used. Instead of volume, pressure values were used instead. Why is pressure used instead of the volume? They both change, so how would I go about determining which variation of the work equation to use? Also, in the solution it appears that the equation is w= -nRTln(p1/p2) why are the pressure values not the other way around (p2/p1)??

[anatorres1B]

Also, is it still possible to use the volume variation instead? I used it the first time around and came out with the same answer.

[Marie_Bae_3M]

Yes, I believe you can use either one. w=-nRTln(p1/p2) is basically found from the original w=-nRTln(v2/v1). This goes back to boyle's law p1v1=p2v2. In other words, v2/v1=p1/p2 (pressure and volume are inversely related to each other) and you plug this into the original equation.

[anatorres1B]

Thank you so much!