Reversible processes [processes which may be made to proceed in the forward or reverse direction by the (infinitesimal) change of one variable], ultimately reach a point where the rates in both directions are identical, so that the system gives the appearance of having a static composition at which the Gibbs energy, G, is a minimum. At equilibrium the sum of the chemical potentials of the reactants equals that of the products, so that: \[\Delta G_{\text{r}} = \Delta G_{\text{r}}^{o}+R\ T\ \ln K=0\] \[\Delta G_{\text{r}}^{\,\unicode{x26ac}} = -R\ T\ \ln K\] The equilibrium constant, K, is given by the mass-law effect.