Final answer:
The general equilibrium expression for an acid is [H+][A-] / [HA].
Step-by-step explanation:
The general equilibrium expression for an acid can be written as:
[H+][A-] / [HA]
This expression represents the ionization of an acid, where [H+] represents the concentration of the hydrogen ion, [A-] represents the concentration of the conjugate base, and [HA] represents the concentration of the acid.