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.