Final answer:
To deduce the direction of acid-base equilibrium, follow the general rule that equilibrium favors the formation of a weaker acid and base from a stronger acid and base. The equilibrium arrows' lengths reflect concentration dominance, and at equilibrium, the rates of forward and reverse reactions are equal.
Step-by-step explanation:
To determine the direction of acid-base equilibrium, we must first understand that according to the Brønsted-Lowry theory, a stronger acid tends to react with a stronger base to produce a weaker acid and base. An equilibrium reaction, represented with double arrows to signify that both forward and reverse reactions happen simultaneously, will favor the direction in which the weaker acid-base pair is formed.
In practical terms, if you see a reaction like HCl reacting with NaOH to form H2O and NaCl, because HCl is a strong acid and NaOH is a strong base that form a weaker acid (H2O) and a weak base (NaCl), the equilibrium will greatly favor the products. Similarly, in a titration curve, before the midpoint, the reaction favors the dissociation of the weak acid (Ka), and after the midpoint, it favors the reaction of the conjugate base with water.
When approaching equilibrium, the rates of the forward and reverse reactions change until they become equal, at which point equilibrium is achieved. This is reflected in the relative lengths of the arrows in equilibrium expressions, where a longer arrow points in the direction where the stronger components are reacting to form weaker ones, until their concentrations become equalized.