The present invention provides a process for preparing 1,1,1,2,2-pentafluoropropane (245cb), the process comprising gas phase catalytic dehydrochlorination of a composition comprising 1,1,1-trifluoro-2,3-dichloropropane (243db) to produce an intermediate composition comprising 3,3,3-trifluoro-2-chloro-prop-1-ene (CF3CCI═CH2, 1233xf), hydrogen chloride (HCI) and, optionally, air; and gas phase catalytic fluorination with hydrogen fluoride (HF) of the intermediate composition to produce a reactor product composition comprising 245cb, HF, HCI and air; wherein the process is carried out with a co-feed of air.