What is the effect of temperature on (ionic product of water)?

Solution

The dissociation of water is an endothermic reaction.

2 straight H subscript 2 straight O left parenthesis straight l right parenthesis space space rightwards harpoon over leftwards harpoon space space space straight H subscript 3 straight O to the power of plus left parenthesis aq right parenthesis space plus space OH to the power of minus left parenthesis aq right parenthesis semicolon space space increment straight H space equals space 57.1 space kJ

According to Le-Chatelier’s principle, an increase in temperature will shift the equilibrium towards that direction where absorption of heat (endothermic change) takes place in order to nullify the effect of the rise in temperature i.e. equilibrium shifts in the forward direction producing a large concentration of H₃O⁺ and OH^– ions. Hence K_w increases with the rise in temperature.