All GRE Subject Test: Chemistry Resources
Example Question #3 : Mechanisms And Intermediates
For which of the following acid-base reactions will the equilibrium lie on the left side?
The pKa value indicates how strong an acid is, and acid strength increases as pKa decreases. The side of a reaction with a lower pKa is going to dissociate more, pushing the equilibrium over to the other side. The equilibrium will thus lie on the side with the HIGHER pKa.
Since the pKa of acetic acid (4.76) is higher than the pKa of trifluoroacetic acid (0), the reaction will shift to the left to reach equilibrium.