#2H_2O(l) rightleftharpoons H_3O^+ + HO^-#
The formation of equilibrium quantities of the characteristic cation, the #"acidium"# ion or so-called #"hydronium ion"#, and #"hydroxide"# ion.
At #298*K# this equilibrium has been VERY carefully measured, and the ion product, #K_w=[H_3O^+][HO^-]=10^-14#, and taking #-log_10# of both sides we gets............
#pK_w=pH+pOH=-(-14)=14#.
How do you think #pK_w# would evolve at higher temperatures? Would it increase, decrease, stay the same. Remember that this autoprotolysis is manifestly a #"bond-breaking reaction"#.
