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 supply " placeholder" thermodynamic data for the surface species to satisfy the requirement.
Note: 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. They may, however, be used in surface heat balances if such are enabled for a particular reacting-flow problem.
The data may be extracted from a database file (for example, therm.dat) and/or read directly from the Surface Kinetics input file. Details on the thermodynamic data format, whether including in the Surface Kinetics input file or in a thermodynamic database file, are provided in Thermodynamic Data Format .
For multiphase chemistry, thermodynamic data are given in a different form described in
Liquid Species in the Chemkin Theory Manual
. Properties for all the liquid species defined in
SITE and BULK must have corresponding data in the
LIQPROPERTIES block.
Note: When thermodynamic data is included in the
Surface Kinetics
Input file, it must immediately follow phase (SITE
and BULK) data.