8.3b


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Annie Lieu-1H
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8.3b

Postby Annie Lieu-1H » Tue Jan 16, 2018 5:25 pm

Hi could someone please explain why for question 8.3 b (which asks if the work with respect to air in the pump is positive or negative) the answer is positive?

If the work is positive because you need more work to compress air (not sure if this is why), in which instances would work be negative?

Hannah Chew 2A
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Re: 8.3b

Postby Hannah Chew 2A » Tue Jan 16, 2018 5:41 pm

Work acts on the system, so if the volume is compressed, then work is being done on the system. Therefore, work is positive. However, if the volume expands, then work would be negative.

Annie Lieu-1H
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Re: 8.3b

Postby Annie Lieu-1H » Tue Jan 16, 2018 11:06 pm

@Hannah

so then please explain why for 8.11 the more negative work answer "does more work"...

Hannah Chew 2A
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Re: 8.3b

Postby Hannah Chew 2A » Tue Jan 16, 2018 11:41 pm

8.11 asks which process does more work, so this question specifically tells us to look at work from the point of view of the system itself, not the surroundings. So using the formula, we would still conclude that reversible expansion produces a more negative work than irreversible expansion. Since we want to look at which reaction does more work on the surroundings, then we would want the more negative answer. I believe the tricky part of work is looking at the point of view, as denoted by the question.


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