# How is the chemical equation for a strong acid dissociated in water different than that for a weak acid?

Jul 25, 2014

We write the equation for the dissociation of a weak acid as an equilibrium reaction, while the dissociation of a strong acid goes to completion.

Most weak acids have ${K}_{\text{a}}$ < 10⁻².

For example, acetic acid has ${K}_{\text{a}}$ = 1.76 × 10⁻⁵.

We write the equation for the dissociation of acetic acid with an equilibrium arrow:

CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺

Most strong acids have ${K}_{\text{a}}$ > 10².

For example, hydrochloric acid has ${K}_{\text{a}}$ = 1.55 × 10⁶.

We write the equation for the dissociation of HCl with an reaction arrow pointing to the right:

HCl + H₂O → H₃O⁺ + Cl⁻