The present process relates to a method for minimizing the formation of 1,1,1,2,2-pentafluoropropane in a liquid phase reaction of 2-chloro-3,3,3-trifluoropropene and HF in the presence of a hydrofluorination catalyst comprising: (a) reacting HF with sufficient amount of 2-chloro-3,3,3-trifluoropropene in the presence of a hydrofluorination catalyst under conditions effective to form 2-chloro-1,1,1,2-tetrafluoropropane, the hydrofluorination catalyst being present in sufficient amounts to catalyze said reaction and the 2-chloro-1,1,1,2-tetrafluoropropane being formed with both a conversion of greater than 80% and a 1,1,1,2,2-pentafluoropropane selectivity lower than 20%; and (b) maintaining the 2-chloro-1,1,1,2-tetrafluoropropane being formed with both a conversion of about 80% or more and a 1,1,1,2,2-pentafluoropropane selectivity of about 20% or less by adding said hydrofluorination catalyst to the reactor in small increments.