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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: confusedstud on August 23, 2015, 03:59:41 AM

Title: Why is ΔG the maximum non expansion work?
Post by: confusedstud 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

Title: Re: Why is ΔG the maximum non expansion work?
Post by: cseil 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'