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Topic: Why is ΔG the maximum non expansion work?  (Read 1780 times)

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Offline confusedstud

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Why is ΔG the maximum non expansion work?
« on: August 23, 2015, 03:59:41 AM »
Is there a way to show that it is the maximum non expansion work? I was thinking delta U=q+w and the w is replaced with the ΔG?

I'm not very sure how do we relate it back to internal energy.

Thanks

Offline cseil

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Re: Why is ΔG the maximum non expansion work?
« Reply #1 on: August 24, 2015, 08:25:12 AM »
G=H-TS

So you can write

dG = dU + pdV + Vdp - TdS - sdT

If T and P are constant:

dG= dU + pdV - Tds

Now dU is q+w+w' where w is the expansion work (-pdV) and w' is the non-expansion work.

dG = q-pdV+w'+pdV -Tds
dG= q+w'-Tds

but q=Tds (rev) or q>_Tds

so

dG = w'

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