# Standard Gibbs energy change definition

by Maylis
Tags: definition, energy, gibbs, standard
 PF Gold P: 457 Hello I am working on deriving the expression relating the equilibrium constant K to the change in Gibbs energy. This part seems to be followed okay, but here I am not following why the change in Gibbs energy of reaction is defined this way. I can see why K is defined in a way because it's just easier to write K than the whole expression. I'm troubled by the fact that I can define something physical like the change in gibbs energy of a reaction. This definition has more meaning than simply that it's easier to write, but I'm not quite coming to the intended conclusion.
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PF Gold
P: 5,046
 Quote by Maylis Hello I am working on deriving the expression relating the equilibrium constant K to the change in Gibbs energy. Attachment 69123 This part seems to be followed okay, but here Attachment 69124 I am not following why the change in Gibbs energy of reaction is defined this way. I can see why K is defined in a way because it's just easier to write K than the whole expression. I'm troubled by the fact that I can define something physical like the change in gibbs energy of a reaction. This definition has more meaning than simply that it's easier to write, but I'm not quite coming to the intended conclusion.
The motivation is this: If you know the free energies of formation of the reactants and products participating in any reaction, then you can calculate the equilibrium constant. On the other hand, if you wanted to tabulate equilibrium constants, then you would have a table of a zillion items because each reactant or product could participate in a huge number of reactions. But, by tabulating the free energies of formation of the substances, the amount of data you need to tabulate is much more limited, especially for common substances. That's why tabulation of the free energies of formation of substances is so useful and convenient.

Chet

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