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

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Answer 1 · 2014-07-25T21:43:31

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_"a"# < 10⁻².

For example, acetic acid has #K_"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_"a"# > 10².

For example, hydrochloric acid has #K_"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⁻