Water molecules undergo autoionization, a reversible equilibrium reaction in which one water molecule transfers a proton to another, producing hydronium (H3O+) and hydroxide (OH-) ions; because the solvent itself is a reactant, the equilibrium expression omits the water concentration term and is defined solely by the product of ion concentrations, yielding the equilibrium constant Kw. This belongs to chemical equilibrium theory within acid-base chemistry, where the "p" notation (negative base-10 logarithm) is used to convert extremely small equilibrium and ion concentration values into convenient linear scales, giving rise to pKw, pH, and pOH. These formalisms establish the quantitative foundation for defining acids and bases by how they perturb the hydrogen ion concentration relative to neutral water.
Water molecules undergo autoionization, a reversible equilibrium reaction in which one water molecule transfers a proton to another, producing hydronium (H3O+) and hydroxide (OH-) ions; because the s…