The free energy change, or ΔG, of a particular reaction is the sum of the standard free energy and RT times the natural log of the ratio of the concentrations of products to reactants. If the ΔG of a reaction is negative, then the reaction progresses forward. The ΔG becomes less negative as the concentrations of the reactants decrease, and that of the products increase. Eventually, the ΔG equals zero when the reaction reaches equilibrium, where the forward and reverse reaction rates are equal. At equilibrium, the ratio of the concentration of products and reactants equals the equilibrium constant, K. The equation can be rearranged to show the mathematical relationship between ΔG0 and K.