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### Topic: What is the difference between reaction Gibbs energy and Gibbs energy?  (Read 430 times)

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#### rentj

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##### What is the difference between reaction Gibbs energy and Gibbs energy?
« on: June 21, 2024, 04:54:37 AM »
I read in my physical chemistry textbook that Gibbs energy ΔG = ΔH - TΔS, however later in the book, I found another quantity, which is reaction Gibbs energy, denoted with ΔrG. I am confused between the differences since the book stated that the reaction Gibbs energy is the slope of the Gibbs energy plotted against the extent of the reaction, dξ. It is said that if the reaction Gibbs energy, ΔrG < 0, the reaction is spontaneous or exergonic. However in other sources, I saw that if the change in Gibbs energy ΔG < 0, the reaction is also exergonic. Isn't that mean that ΔrG and ΔG are both the same quantity? Thank you.

#### mjc123

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##### Re: What is the difference between reaction Gibbs energy and Gibbs energy?
« Reply #1 on: June 21, 2024, 06:26:46 AM »
I'd recommend looking at this thread: https://www.chemicalforums.com/index.php?topic=87048.0, and the thread I quote inside it.
Note that there are some differences in notation between different sources.
ΔG < 0 (as you define ΔG) means that the conversion of pure A to pure B is exergonic.
ΔrG < 0 (as you define ΔrG) means that it is spontaneous for the reaction to proceed in the direction of increasing ξ from where it is.
A graph such as in those threads should make this clearer.
« Last Edit: June 21, 2024, 11:04:22 AM by Borek »