Water Autoionization

H2O + H2O ⇌ H3O+ + OH−

Übersicht

Water undergoes autoionization where one molecule acts as an acid (donates H⁺) and another acts as a base (accepts H⁺). The equilibrium constant Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 C, defining pH 7 as neutral. This endothermic reaction shifts right at higher temperatures, decreasing neutral pH.

Teilnehmer

Rolle Substanz Koeffizient Zustand
Reaktant Water H₂O 2 (l)

Alltägliches Beispiel

The pH scale itself is defined by water autoionization, which is why pH 7 is neutral at 25 C and why neutral pH changes at different temperatures.

Industrielle Bedeutung

Understanding Kw is fundamental to all aqueous chemistry, pH measurement, water quality analysis, and buffer design.

Eigenschaften

Typ
Acid-Base
Reversibel
Ja
Energie
Endotherm
ΔH
55,8 kJ/mol

Verwandte Reaktionen

Hydrochloric Acid and Barium Hydroxide Acetic Acid and Sodium Acetate Buffer System Acetic Acid Dissociation in Water Ammonia and Hydrochloric Acid Ascorbic Acid and Sodium Hydroxide Barium Hydroxide and Ammonium Thiocyanate (Endothermic) Carbonic Acid and Sodium Hydroxide Aluminum Hydroxide as Amphoteric Acid with NaOH Aluminum Chloride and Chloride Ion (Lewis Acid-Base) Formic Acid and Sodium Hydroxide

Frequently Asked Questions

What is the equation for Water Autoionization?
The balanced equation is: H₂O + H₂O ⇌ H₃O⁺ + OH⁻.
What type of reaction is Water Autoionization?
Water Autoionization is a acid-base reaction. It is reversible under certain conditions.
Is Water Autoionization exothermic or endothermic?
Water Autoionization is endothermic (absorbs energy). The enthalpy change (ΔH) is 55.8 kJ/mol.