# Instantaneous enthalpy and entropy change of reaction as equilibrium is established

Can we calculate instantaneous difference between enthalpy and entropy of product and reactants of a reaction as the reaction proceeds towards equilibrium? Ex: $\ce{R<->P}$ reaction, at some reaction coordinate, moles of $R = 1-x , P = x$, Enthalpy difference between products and reactants? Enthalpy difference if it reached equilibrium? Values of $$\Delta G^0, \Delta H^0, \Delta S^0$$ are known. Or is it impossible and the only relationship available is $$\Delta H = T \Delta S$$ at equilibrium or are their values only temperature dependent and activity independent?

We can do this for Gibbs free energy by $$\Delta G=\Delta G^0+\mathcal RT\ln Q$$

• In order to do this, you need to accept the idea that the thermodynamic functions and be defined and calculated even for non-equilibrium states of a system. I have no problem accepting this, but certainly some physicists would not be willing to make this leap. – Chet Miller Dec 16 '16 at 15:38
• G is also a thermodynamic function right? – Mrigank Dec 17 '16 at 0:31
• Sure G is a thermodynamic function. – Chet Miller Dec 17 '16 at 2:54
• en.m.wikipedia.org/wiki/Partial_molar_property It seems that Chemical Potential is bridging the gap and it's only connection is to G. H needs entropy to be constant. Any thoughts? – Mrigank Dec 17 '16 at 5:23
• I agree with everything in the reference you provided. G is the most useful and convenient function for defining the chemical potential. In fact, the chemical potential is just the partial molar Gibbs free energy. – Chet Miller Dec 17 '16 at 12:35