When a Reaction is defined, a Species node () is automatically generated for the participating reactants and products. This feature enables you to review and enter species specific information regarding chemical kinetics, thermodynamics and transport properties.

It is also possible to add and define an individual Species node: on the Reaction Engineering toolbar click Species or right-click the Reaction Engineering node and select it from the context menu.

When a Species node is automatically generated using the Formula text field in the Reaction node, the species name is also automatically generated.

For a Species node added individually, enter a Name in the field and click Apply. By entering a name consisting of only elements from the periodic table, the chemical formula is added, and molar mass is calculated and added in the Chemical Formula section. The species charge, and type, are also deduced from the species name.

Select a species type — Bulk species, Surface species, or Solvent.

Bulk species are solved for volumetric concentrations (SI unit: mol/m3), while Surface species are solved for surface concentration (SI unit: mol/m2). The compositions for Bulk species and Solvent (not solved for) use the syntax c_speciesname, while Surface species uses csurf_speciesname_surf.

Surface species is referring to species adsorbed on a reactive surface. When Surface species is selected, the corresponding reaction formula introduces (ads) after the species notation and changes the species’ name to speciesname_surf. Additionally, the Species node name is updated in a similar fashion.

For the Plug flow reactor only Bulk species and Solvent are allowed.

The Chemical Formula section contains the species chemical formula, Molar mass, M, and Charge, z.

If the name entered for the species consists of only elements from the periodic table, and optionally charge and phase indication, then the Chemical Formula field will be populated with the name entered in the Name section, and the molar mass and charge will be added to this section. The species molar mass is computed from the mass of occurring individual elements¹. The rules for writing chemical formulas are the same as those for Species names.

When the species name contains parts not in the periodic table, for example when a descriptive name such as water is used, the molar mass is set to 0.0 kg/mol. If the species name consists of a valid charge or phase indication, then charge and type will be set automatically. In this case, the molar mass needs to be defined in order to achieve mass balanced reactions and correct definitions of mass basis properties. By entering a chemical formula consisting only of elements from the periodic table (and optionally charge and phase indication), the molar mass, and charge are derived automatically.

When needed, the Molar mass can be edited in the corresponding text field. Editing the Chemical formula and pressing apply will override the content in the molar mass and charge fields. The Charge field cannot be edited as long as a chemical formula is enabled.

With an enabled Chemical Formula it is possible to use the trivial name of a species and balance reactions. Having added the Species water, oxygen, and hydrogen, and filled in H2O, O, and H in their respective chemical formula sections, the Formula oxygen+hydrogen=water is balanced into oxygen+2hydrogen=water by clicking Balance in the Reaction node.

It is possible to specify the species density ρ when the fluid Mixture is specified as Liquid. The default value is that of water at 293 K.

Change the Automatic default setting to User defined to use a species reaction rate other than the one set up in the associated Reaction node. For individual species, use the User defined option to set a reaction rate other than zero (that is, nonreactive).

Edit either the Rate expression (SI unit: mol/(m3s)), the Surface rate expression (SI unit: mol/(m2s)), or both. For a bulk species, both expressions appear if surface reactions are present in the reactor since the reaction of the species can depend both on bulk reaction R and surface reaction Rads rates. For a surface species, only the surface reaction rate Rads appears.

The reaction rate is not editable if the species in question participates in an equilibrium reaction and has been selected as a Predefined dependent species in Equilibrium Species Vector.

To account for nonideality in the fluid mixture adjust the activity coefficient in the Activity coefficient text field here. The section is only shown if activity instead of concentration has been chosen in the interface; that is, the Use activities check box is selected on the Reaction Engineering interface Settings window

Click to select the Keep concentration/activity constant check box if the species concentration or activity should be treated as constant.

Here the required parameters to compute various transport properties can be edited. To show this section the Calculate mixture properties check box needs to be selected under the Calculate Transport Properties section on the physics interface Settings window.

The parameters utilized for calculation of thermodynamic mixture and reaction properties are set in this section. It is accessed when the Energy Balance is set to Include for the Reaction Engineering interface, in other words, for nonisothermal conditions.

The Thermodynamic Expressions are by default computed using data in the NASA format. In this case, enter the following to compute the species’ heat capacity, Cp (SI unit: J/(mol⋅K)), the molar enthalpy, h (SI unit: J/mol), and the molar entropy, s (SI unit: J/(mol⋅K)):

Any coefficients for the thermodynamic polynomials entered into the alow,k fields apply to the temperatures in the range Tlo to Tmid; coefficients entered into the ahi,k fields apply to temperatures in the range Tmid to Thi range. The coefficients can also be imported in the CHEMKIN Import for Species Properties section in the Reaction Engineering node.

Choose the User defined alternative to specify Cp, h, and s directly.