Standard Gibbs energy change definition

[gfd43tg]

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.

 

[Chestermiller]

Hello

I am working on deriving the expression relating the equilibrium constant K to the change in Gibbs energy.

View attachment 69123

This part seems to be followed okay, but here

View 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