I recently learned about the standard Gibbs free energy change of reaction, ΔG=ΔH-TΔS, and how its sign indicates whether the conversion of (ALL) reactants and products is spontaneous or not.
I then learned that the equilibrium constant of a reversible reaction depends on ΔG for some reason.
The equation shows that whether a reaction goes is (noticeably) reversible or effectively goes to completion depends on how -ve ΔG is.
Given the relationship between ΔG and K, is there any explanation of why reactions are reversible in the first place?
If a reaction is exergonic and the 100% conversion of reactants to products would increase total entropy, why shouldn't it go to completion?
If a reaction is endergonic and the 100% conversion of reactans to products would decrease total entropy, why should it occur to any extent at all?