## G=H-TS

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Liam Maxwell 2E
Posts: 53
Joined: Fri Sep 29, 2017 7:07 am

### G=H-TS

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

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

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

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

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