I just got introduced to this concept and these thoughts came into my mind. Is there a way to increase the equilibrium constant of the autoionization of water?

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    $\begingroup$ Are you talking about the rate (kinetics) or the equilibrium position (thermodynamics)? $\endgroup$ Jun 9, 2018 at 11:46
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    $\begingroup$ Heat it. Autodissociation is an endohermic reaction. $\endgroup$ Jun 9, 2018 at 11:48
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    $\begingroup$ As a follow on from @Oscar Lanzi, supercritical water can start to pit/corrode steel due to the increased ionisation causing increased acidity. $\endgroup$
    – Beerhunter
    Jun 10, 2018 at 19:11

1 Answer 1


First of all, I'm assuming you mean the equilibrium position. This is not the same as the rate of the reaction.

Sure there is. The easiest way to increase the equilibrium position water's ionization is by heating it.

To find out how much increasing the temperature of water will affect $K_w$, the Arrhenius equation will work for values of $T$ close to $0 °C$. $K_w=Ae^{\frac{-E_a}{RT}}$.

Of course, you'll have to find $A$ from experimental data.

Here is a graph of how changing the temperature affects $pK_w$. For the most part, as temperature increases, you will see an increase in K.


  • $\begingroup$ The curve turns around because of the effect of decreasing density of the (supercritical) water at higher temperatures. Is there a similar curve at constant density available? $\endgroup$ Jun 13, 2018 at 9:13
  • $\begingroup$ @OscarLanzi you are right. I'm not sure if there is a graph at constant density, but I will look for one. $\endgroup$
    – Neil
    Jun 13, 2018 at 17:37

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