Kinetic and mechanistic studies of the isomerization reactions of 1,1,2,2-tetrafluoroethane to 1,1,1,2-tetrafluoroethane on conditioned chromia were carried out. In contact with the surface of the solid 1,1,2,2-tetrafluoroethane undergoes a separation of HF, forming noticeable amounts of the olefin trifluoroethylene. Due to rearrangement of the adsorbed gas molecules in the surface, HF is re-added, forming 1,1,1,2-tetrafluoroethane according to the Markovnikov rule. CHF2-CHF2 reversible arrow CHF=CF2 + HF CHF=CF2 + HF reversible arrow CH2F-CF3 A mathematical adjustment was carried out in order to describe the reaction mechanism. Modelling of the isomerization reaction suggests that the best agreement between the experimental and the calculated data can be achieved when the decomposition of CHF2-CHF2 to HF and CHF=CF2 is considered to be reversible. The experimentally determined values of rate constants indicate a significant influence of the adsorption equilibria on these reactions.