## Explain Figure 9.25...

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

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

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

Annie Lieu-1H
Posts: 68
Joined: Fri Sep 29, 2017 7:04 am
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### Explain Figure 9.25...

Hi, I'm very confused by what Figure 9.25 in the textbook is trying to tell us.

And the attached paragraph is really confusing and convoluted..

Would anyone be able to summarize the information the graph is trying to tell in regards to Gibbs free energy and phase changes??

Andres Reynoso 1J
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: Explain Figure 9.25...

The graph is essentially showing us the relationship between temperature and the (molar) Gibbs free energy of a substance at a given pressure and how they both correlate to what phase a certain substance in in. It shows us that at low temperatures, the Gibbs free energy is lowest for solids. Because the solid phase line has the lowest Gibbs free energy at this point, there is a tendency for the substance to spontaneously freeze and become a solid. At a certain higher temperature (the first dotted line where the "liquid stable" region begins), the Gibbs free energy for the liquid phase has passed the solid line and is the lowest, so there will be a spontaneous tendency for the substance to melt and become a liquid. At higher temperatures (the beginning of the "vapor stable" region), the vapor line has gone below the liquid line and the vapor phase now has the lowest Gibbs free energy at that temperature; therefore, there will be a spontaneous tendency for the substance to vaporize.
I hope this helps.

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