This reaction has been employed as a means of assaying copper(II) samples, since the evolved I2 can be analyzed by redox titration. The reaction in itself may look rather odd, as using the rule of thumb for a proceeding redox reaction, Eooxidator − Eoreductor > 0, this reaction fails. The quantity is below zero, so the reaction should not proceed. But the equilibrium constant for the reaction is 1.38*10−13. By using fairly moderate concentrates of 0.1 mol/L for both iodide and Cu2+, the concentration of Cu+ is calculated as 3*10−7. As a consequence, the product of the concentrations is far in excess of the solubility product, so copper(I)iodide precipitates. The process of precipitation lowers the copper(I) concentration, providing an entropic driving force according to Le Chatelier's principle, and allowing the redox reaction to proceed.