Which equilibrium expression represents the ionization of water?

The equilibrium constant expression for this reaction that takes place in water and involve ions can be written as K=  [H_3 O^+ ][OH^- ]/([H_2 O]  ^2 ). But the concentration of undissociated water, H_2 O is much larger than the concentration of the ions that is essentially remains constant. Therefore, we can include it in the equilibrium constant. The resulting new equilibrium constant can be written:  K_W= [H_3 O^+ ][OH^- ].

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frequency, z, and the collision density, z, in carbon dioxide (co2), r 180 pm at 30 °c and 120 kpa