∆G, ∆H, ∆S






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Donna Nguyen 2L
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Joined: Sat Aug 24, 2019 12:17 am

∆G, ∆H, ∆S

Postby Donna Nguyen 2L » Tue Feb 11, 2020 1:13 am

What's the relationship between ∆G, ∆H, and ∆S? I know that the Gibbs Free Energy equation is ∆G = ∆H - T∆S, but I'm not sure how exactly it all fits together.

Ashley Tran 2I
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Joined: Thu Jul 11, 2019 12:17 am

Re: ∆G, ∆H, ∆S

Postby Ashley Tran 2I » Tue Feb 11, 2020 8:49 am

Based on where we are in class, this has been the only relationship established. You can also think of how relative the values of ∆H and ∆S make ∆G negative at which temperatures to determine whether a reaction is spontaneous.

Kassidy Ford 1I
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Re: ∆G, ∆H, ∆S

Postby Kassidy Ford 1I » Tue Feb 11, 2020 4:39 pm

^^ as they said above, in order for a spontaneous reaction to occur, deltaG must be negative. This means that the value for T*deltaS must be greater than the change in enthalpy. For an endothermic reaction where enthalpy is a positive number this is often not true except at very high temperatures.

Megan Kirschner
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Joined: Wed Feb 20, 2019 12:17 am

Re: ∆G, ∆H, ∆S

Postby Megan Kirschner » Tue Feb 11, 2020 6:38 pm

They relate because they can tell you lots of things about if a reaction will occur spontaneously and if it's favorable. It is expected that how this could be presented on a test would be if you were given all or some of these terms and asked to deduce overall conclusions about the system.

Bryan Chen 1H
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Re: ∆G, ∆H, ∆S

Postby Bryan Chen 1H » Tue Feb 11, 2020 7:03 pm

basically, deltaG depends on deltaH and deltaS to be a spontaneous(-) or nonspontaneous(+) rxn. Since it is a new topic i dont think we need to know much more than that

Eva Zhao 4I
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Joined: Sun Sep 29, 2019 12:16 am

Re: ∆G, ∆H, ∆S

Postby Eva Zhao 4I » Wed Feb 19, 2020 6:42 pm

Here's a table that relates the three fairly well, with respect to T in order to determine spontaneity:
Image

Justin Quan 4I
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Re: ∆G, ∆H, ∆S

Postby Justin Quan 4I » Wed Feb 19, 2020 6:49 pm

To add on, ∆G = ∆H - T∆S is very useful for predicting if a given reaction is spontaneous or non-spontaneous. When ∆G=0 the system is at equilibrium. When ∆G is negative, the forward reaction is spontaneous. When ∆G is positive, the reverse reaction is spontaneous. The sign of ∆G depends on the enthalpy, entropy, and temperature; Its relationship is modeled by the equation ∆G = ∆H - T∆S.


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