G=H-TS






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Liam Maxwell 2E
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Joined: Fri Sep 29, 2017 7:07 am

G=H-TS

Postby Liam Maxwell 2E » Tue Jan 30, 2018 11:37 pm

The book says that the higher the temperature the less positive the Gibbs free energy, but isn't that not 100% correct? Looking at the formula G=H-TS if H is positive and S is negative then a higher temperature would actually result in a higher value of G

Morgan Baxter 1E
Posts: 50
Joined: Thu Jul 27, 2017 3:00 am

Re: G=H-TS

Postby Morgan Baxter 1E » Wed Jan 31, 2018 12:18 am

You are correct. When H is positive and S is negative, having a high temperature will increase G. In fact, since this equation is uses temperature in K, there can't be a negative temperature, so in these conditions, the G will always be positive. The book must have been referring to a case in which S was positive.

Dang Lam
Posts: 55
Joined: Thu Jul 27, 2017 3:01 am

Re: G=H-TS

Postby Dang Lam » Thu Feb 01, 2018 5:30 pm

Yes, Dr.Lavelle actually went over all the cases in which delta G can be both positive and negative

Jimmy Zhang Dis 1K
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

Re: G=H-TS

Postby Jimmy Zhang Dis 1K » Fri Feb 02, 2018 3:20 am

As a general guideline for deltaG:
+deltaS and -deltaH means spontaneous at all temp
+deltaS and +deltaH means spontaneous at high temp
-deltaS and-deltaH means spontaneous at low temp
-deltaS and +deltaH means not spontaneous at all

Emma Miltenberger 2I
Posts: 51
Joined: Thu Jul 27, 2017 3:00 am

Re: G=H-TS

Postby Emma Miltenberger 2I » Sun Feb 04, 2018 3:08 pm

Lavelle clarified this in lecture. As a general rule of thumb:
+deltaH and +deltaS= spontaneous at high temperatures
+deltaH and -deltaS=not spontaneous
-deltaH and +deltaS= spontaneous at all temperatures
-deltaH and -deltaS= spontaneous at low temperature


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