What is the chemical equation representing how water split into hydrogen ions and hydroxide ions?

Answer 1

The corresponding reaction to the equilibrium is;

H2O(l) <-> H+(aq) + OH-(aq) or another interpretation is;

2H2O(l) <-> H3O+(aq) + OH-(aq)

Answer 2

The chemical equation for the ionization of water is: H2O ⇌ H+ + OH-. This represents the equilibrium reaction where water molecules can dissociate into hydrogen ions (H+) and hydroxide ions (OH-).