An acid that would produce an equilibrium favoring the reactants when reacted with C5H7COOK (aq) is a weak acid. In general, weak acids have a lower tendency to dissociate in solution, resulting in a higher concentration of the acid in the equilibrium mixture. This higher concentration of the acid would push the equilibrium towards the reactants side. Examples of weak acids that may favor the reactants in this reaction could be acetic acid (CH3COOH) or formic acid (HCOOH).
