Practice Problem

$w=-P\Delta V$
and
$w=-\int_{V_{1}}^{V_{2}}PdV=-nRTln\frac{V_{2}}{V_{1}}$

Michelle Steinberg2J
Posts: 73
Joined: Fri Sep 29, 2017 7:04 am

Practice Problem

I am confused why the value of work is negative in this answer. The equation that I set up was
982J=492J + w
because it says the internal energy increased (positive value) and the system absorbed heat (positive value). I would think that work is done on the system because I got a positive value.

If someone could explain why the correct answer is negative, that would be really helpful. Thanks!
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Andres Reynoso 1J
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

Re: Practice Problem

I think you're correct Michelle and agree with your conclusion; the value should be positive because of $\Delta U=q+w$. Additionally, part b should be work done on the system. Perhaps a typo in the question? Typo could make sense given the 982 kJ - 492 kJ = +490 kJ, not 491... I think you're correct, but someone feel free to let us know if it should actually be negative.

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