The most common equation for the self ionization of water I've seen is with protons and hydroxyl ions as products.

H2O ⇌ H+ + OH-

I've also seen the following equation with hydronium ions as a product instead of protons

2H2O ⇌ H3O+ + OH-

Does the first equation actually happen, or is it just an abbreviation for the second? Or do both species (hydronium and protons) exist in solution, or something more complicated?

  • $\begingroup$ Bare protons do not exist in chemistry. First form is a shorthand for the second. $\endgroup$ Oct 9, 2017 at 13:54
  • 2
    $\begingroup$ Ivan is right but technically even the second equation is a short hand for how acidic protons are held by a whole network of H2O. $\endgroup$
    – Tyberius
    Oct 9, 2017 at 14:16


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