Self-Ionization (Water Equilibrium)

Shows water reacting with itself to form hydronium and hydroxide, the source of the intrinsic ions in pure water and the basis for Kw.

$$2{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}+\mathrm{O}{\mathrm{H}}^{-}$$

Variables

Symbol	Meaning	Unit
${\mathrm{H}}_3{\mathrm{O}}^{+}$	Hydronium ion	mol/L
$\mathrm{O}{\mathrm{H}}^{-}$	Hydroxide ion	mol/L

Worked example

About one molecule in 555 million is split into ions at any instant in pure water at 25 C.

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Part of The Blueprint of Water