variavel0=<b>Ângela Patricia Spilimbergo</b> - patspi@unijui.tche.br UNIJUÍ
<b>Raísa L. Iskhakova</b> - kriukov@unijui.tche.br UNIJUÍ
<b>Cleusa J. Auth</b> - cleusa@unijui.tche.br UNIJUÍ
<b>Abstract.</b> The current software employed to determine the properties of the chemical equilibrium systems had its origin  in the 70`s and has been carried out in its latest versions in the "FORTRAN 77" medium. In this study the software  "Chemical Equilibrium Processes" is presented as it was created to be carried out in the "FORTRAN 90" medium.  Using the same mathematical basis of the previous version, operators and functions of the type "dynamic allocation",  free  format,  syntactic  analysis,  etc,  were  incorporated  into  the  latter.  As  a  result,  the  software  has  become  more  accessible to  the user. The study describes the procedures for the symbolic transformations: reading and syntactic  analysis of the strings of symbols of the  chemical substances, splitting  of  these symbols, reordering of the  kinds  of  substances, forming the vectors and matrices necessary for "building" the chemical equilibrium equations, etc. The  study also shows the advantages of the software new version in the examples relative to the computation of the  thermodynamical and thermophysical characteristics of the combustion resulting products for a complex reagent  medium such as "coal + air + CaCO3*" and the propellent: "natural gas + air + O2".
<b>Keywords.</b> software, chemical equilibrium, data analysis, pollutants, Fortran 90.