HW 8.47

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Alyssa McLeod 3E
Posts: 13
Joined: Wed Sep 21, 2016 2:59 pm

HW 8.47

Postby Alyssa McLeod 3E » Sun Jan 22, 2017 12:42 pm

For a certain reaction at constant pressure, , and 35kJ of expansion work is done by the system. What is for this reaction?

I got the correct answer by using the formula but when I checked my answer via an old post here on chemistry community, someone made the point that work should be negative because and the volume change must be positive because expansion occurs. But plugging a negative work into the equation yields the wrong answer, so what am I missing? (Note: I don't have the solutions manual, so my answer (7kJ) could just be wrong?)

Rachel Kipp 1I
Posts: 16
Joined: Wed Sep 21, 2016 2:55 pm

Re: HW 8.47

Postby Rachel Kipp 1I » Sun Jan 22, 2017 2:30 pm

so and which , since the work is done ON the system. We also know from the givens in question 47

Plug in this info and you will get,

nicoleclarke_lec1M
Posts: 25
Joined: Sat Jul 09, 2016 3:00 am

Re: HW 8.47

Postby nicoleclarke_lec1M » Sun Jan 22, 2017 4:36 pm

My book stated that the work done by the system was 22 kJ, so I simply used the formula Δu=q+w, and made the work negative since the work is done BY the system, and therefore the system is losing energy. Also, since the equation is at constant pressure, q is really q sub p, and i used Δu=15+(-22) to get that Δu=7 kJ.


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