The ionization of water can be represented by the following equilibrium reaction:H2O H+ + OH-At 25C, the concentration of H+ ions and OH- ions are equal in pure water. Given the concentration of H+ ions is 1 x 10^-7 M, the concentration of OH- ions will also be 1 x 10^-7 M.The equilibrium constant, Kw, for the ionization of water is calculated as follows:Kw = [H+] [OH-]Substitute the given values:Kw = 1 x 10^-7 M 1 x 10^-7 M Kw = 1 x 10^-14 M^2So, the equilibrium constant, Kw, for the ionization of water at 25C is 1 x 10^-14 M^2.