Simulation of chemical processes is insofar complex that even the latest simulation programs are not sufficiently versatile and so the quality of means for their extension is a significant criterion for their evaluation. The article deals with the extension of the HYSYS simulation program. A typical field is reaction kinetics where we mostly depend on measurement results and own relationships. The implementation of experimental models of reaction kinetics into program is shown on the example of catalytic oxidation of SO₂ to SO₃. The described possibilities of program extension make it a versatile tool for the use in simulation of chemical processes.