Why is Gibbs free energy 0 at equilibrium in a chemical reaction?
the free energy change of the reaction in any state ΔG(when equilibrium has not been attained) is related to standard free energy change of reaction ,ΔG°(which is equal to difference in energies of formation of products and reactants both in their standard state ) according to the equation : ΔG = ΔG° + RT lnQ where Q is reaction quotient .. when equilibrium is attained there is no furthur free energy change i.e. ΔG = 0 ..and Q becomes K (equilibrium constant) ..hence above equation becomes.. 0 = ΔG° + RT ln Q or,ΔG° = -RT ln Q ΔG° is a constant for a particular reaction…as this is the difference (ΣG°f, products – ΣG°f, reactants) The other quantity ΔG, defined by above Equation, represents the total free energies of all substances in the reaction mixture at any particular system composition.
