To the best of my understanding, the quantity of Gibbs free energy of an entity depends on its concentration in the system. Equilibrium is reached when ∆G = 0, or when the Gibbs free energies of all the entities are equal to each other.
If Gibbs free energy is dependent on concentration, then at standard conditions, the concentrations of all entities is 1M—this is fixed by convention. How then can you have a ∆Gº value? All the concentrations are fixed and there is no change in concentration nor energy. Is ∆Gº then just a rudimentary concept for those who do not know calculus? Should it be better written as dGº?
In a similar vein, though slightly unrelated, I would also want to know if enthalpy is related to concentration, similar to how Gibbs free energy is. Why or why not? If enthalpy is also concentration dependent, then does ∆Hº exist?