Gibb's Free Energy

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Audrey Goodman 1F
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Joined: Fri Sep 29, 2017 7:06 am

Gibb's Free Energy

Postby Audrey Goodman 1F » Sat Feb 03, 2018 9:18 pm

What is the main difference between Gibbs free energy of reaction and the standard Gibbs free energy of reaction? I get that the second is in terms of standard molar Gibbs energies, but in lecture, we said that when Gibbs free energy of reaction = 0 the reaction is at equilibrium, but when the standard free energy = 0, it's not. Why is this?

Varsha Sivaganesh 1A
Posts: 51
Joined: Thu Jul 13, 2017 3:00 am

Re: Gibb's Free Energy

Postby Varsha Sivaganesh 1A » Sat Feb 03, 2018 9:37 pm

G° is the change in Gibbs free energy at the standard state, meaning at either 1 atm or 1 M. Also, I think that when G° = 0, the reaction is still at equilibrium... In the example we did in lecture with the Br2(l) turning into Br2(g), we assumed that equilibrium was when G° = 0, and used that to solve for temperature.

Aijun Zhang 1D
Posts: 53
Joined: Tue Oct 10, 2017 7:13 am

Re: Gibb's Free Energy

Postby Aijun Zhang 1D » Sat Feb 03, 2018 10:59 pm

Gibb's free energy is just "G" which is a state function, but standard free energy change is G°, indicating substance in a standard state.

G is the G at equilibrium since G is a quadratic function. Its tangent line at local minimum is G. And at that point, G = 0. But G° is calculated through G. At equlibrium, G°= -RTlnK. If K is equal to 1, then G°=0. If K is not equal to one, then G° will be either positive or negative. But still, G is 0.

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