A method is disclosed for increasing in a composition the mole fraction of a compound selected from the group CF3CHCl2, CF3CHF2 and CF3CHClF relative to the total mole fraction of the other two compounds of the group. The method comprises (a) providing a gaseous composition comprising at least one compound of said group provided that (i) if the selected compound is either CF3CHCl2 or CF3CHF2, said gaseous composition comprises CF3CHFCl and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 50null C., and (ii) if the selected compound is CF3CHFCl, said gaseous composition comprises both CF3CHCl2 and CF3CHF2 and the mole fraction of the selected compound relative to the other two compounds in said gaseous composition is less than its equilibrium amount at 500null C.; (b) contacting said gaseous composition with a catalyst selected from the group of catalysts consisting of catalysts comprising chromium as an oxide, as a halide or as a halided oxide, in a valence state of three to six, and supported catalysts containing at least one metal selected from cobalt, copper, iron, manganese, nickel and zinc for a time sufficient to provide substantial equilibrium between the three compounds having said formula; and (c) providing during said catalyst contact a temperature within the range of about 50null C. to 500null C. at which the mole fraction of the selected compound relative to the other two compounds increases.