Any chemical species that appears in a problem must have thermodynamic data associated with it. This data is used in evaluation of thermodynamic properties (entropy, enthalpy, heat capacity) and reverse reaction rate constants through the equilibrium constant. Often thermodynamic data for a species, for instance a surface species, is unknown. Such data can sometimes be calculated via theoretical techniques. However, the user can work around the need for actual thermodynamic data for all species by making the reactions irreversible. In this case, the user can provide "dummy" thermodynamic data for the surface species to satisfy the Surface Kinetics input requirement and supply the elemental composition of the surface species.
Tip: If every reaction in the mechanism is either irreversible, or if Arrhenius rate parameters are given explicitly for the reverse reaction, then the thermodynamic data for species are not actually used for anything related to the kinetics. However, they may be used for determining heat-capacity or energy-balance effects involving the surface.
Thermodynamic data may be extracted from a database file (therm.dat) and/or read from the Surface Kinetics input file. If all the thermodynamic data are extracted from the database, then no thermodynamic data are required from the input file. However, if the user wishes to override information in the database or provide data on species not in the database, then thermodynamic input is needed in the Surface Kinetics input file. In any case the format for the information is the same, and is described in detail in Thermodynamic Data in the Chemkin Input Manual.
When thermodynamic data input is required, it must immediately follow species data
(SITE and BULK data). The first thermodynamic data line must start with the word
THERMO (or THER). If all the thermodynamic data are input directly to the
Preprocessor, then the first line of this section must read THERMO ALL and the program
will not expect a Thermodynamics Database file; for this option the next line must be
line 2 of
Table 3.1: Summary of the rules for thermodynamic data. For either option, the subsequent thermodynamic data lines must
be in the format of lines 3 -6 of
Table 3.1: Summary of the rules for thermodynamic data. (For the THERMO option the default midpoint
temperature is taken from the second line of information already in the
Thermodynamic Database.) The THERMO input can include as many species as are
needed. Thermodynamic data for any species that were not declared in the SITE and
BULK sections will be ignored. The cases for the thermodynamic data section are the
same as those described in
Thermodynamic Data (Optional)
for Gas-phase Kinetics input.