4.5.2. Reaction Data

Each reaction entry is divided into two fields, (an entry may use multiple lines if it is more than 80 characters long). A reaction data entry is continued on the next line using the special character "& " at the end of the line; any information following the & symbol on the same line is ignored. The first field in the reaction entry contains the symbolic description of the reaction, while the second contains the Arrhenius rate coefficients. Both fields are format free, and blank spaces are ignored. All characters on a line following an exclamation mark (!) are considered comments and are ignored. Blank lines are also ignored.

The reaction description, given in the first field, must be composed of the species symbols, coefficients, and delimiters as summarized below.

Note: Ansys Chemkin 2021 R2 supports limited choice of rate formulations. All liquid and gas-liquid reactions are assumed to be volumetric. Inter-phase reactions involving liquid and solid surface are not supported in 2021 R2.

Reactions for multiphase chemistry follow the same format as described in this section for solid surface reactions. Like solid surface reactions, liquid species can react with gas species, species from the same bulk, and species from other bulks from the same material defined in the kinetics input.

Table 4.4: Surface Reaction Data Criteria

Species Symbols
	Each species in a reaction is described with the unique sequence of characters as they appear in the species data and the thermodynamic data.
Coefficients
	A species symbol may be preceded by an integer or real coefficient. The coefficient has the meaning that there are that many moles of the particular species present as either reactants or products; for example, `2OH` is equivalent to `OH +OH`. The "`#` " symbol is used to mark stoichiometric coefficients that are additionally multiplied by a `YIELD` coefficient. This is explained in Auxiliary Reaction Data .
Delimiters
+	A plus sign is the delimiter between each reactant species and each product species.
=	An equality sign is the delimiter between the last reactant and the first product in a reversible reaction.
<=>	An equality sign enclosed by angle brackets can also be used as the delimiter between the last reactant and the first product in a reversible reaction.
=>	An equality sign with an angle bracket on the right is the delimiter between the last reactant and the first product in an irreversible reaction.

The second field of the reaction line is used to define the Arrhenius rate coefficients , , and in that order, as given by Equation 3–5 of theChemkin Theory Manual . At least one blank space must separate the last species name in the reaction and first number. The three numbers must be separated by at least one blank space, be stated in either integer, floating point, or "E" format (for example, 123 or 123.0 or 12.3E1), and have units associated with them (although the units do not appear on the input line). Unless modified by the REACTIONS line or by the UNITS auxiliary keyword, the default units for are cgs (cm, sec, K, mole), the exact units depending on the order of the reaction. The factor is dimensionless. The default units for the activation energies are cal/mole.

The second field of the reaction line may optionally be used to specify the coefficients a _i, b _i, and c _i of Equation 4–10 of theChemkin Theory Manual for a sticking coefficient. In order for the second field to apply to sticking coefficient parameters, the next line of input must contain the auxiliary keyword STICK.

Examples of some reaction data are shown in Figure 4.5: Examples of Reaction Data . Table 4.5: Summary of the Rules for Reaction Data summarizes the reaction data rules.

Figure 4.5: Examples of Reaction Data

REACTIONS  KCAL/MOLE NONCON
ASH3 + AS(P) <=> ASH3(P) + AS(D)      4.0E11   0 25   ! Ref. 21
! ASH3 + AS(P) <=> ASH3(P) + AS(D)    4.0E11   0  0   ! same as previous
ASH <=> AS(D) + H(S)    1.0   0  0
      STICK
GA(CH3)3(L) + GA2AS(A) <=> AS + GA(CH3)(L) + 2 GAME & ! continued on next line
                                          1.0E13   0  4000.

Table 4.5: Summary of the Rules for Reaction Data

Rule	Description
1	The first reaction line must start with the word `REACTIONS` (or `REAC`), and may be followed by units definition(s), the word `MWON`, `MWOFF`, `NONCON`, or the word `USRPROD`.
2	The word `MWOFF` can be used to turn off the Motz-Wise correction of Equation 4–15 of the Chemkin Theory Manual , for all sticking-coefficient reactions, or the word `MWON` can be used to specify that the Motz-Wise correction is to be used for all sticking-coefficient reactions (the default). Including `MWOFF` or `MWON` as an auxiliary keyword for an individual reaction (discussed later) will override the setting given on the `REACTIONS` line.
3	Valid unit declarations are `EVOLTS`, `KELVINS`, `CAL/MOLE`, `KCAL/MOLE`, `JOULES/MOLE`, `KJOULES/MOLE`, `MOLES`, `MOLECULES, SITEFR, ATM, BAR, DYN, TOR,` and `PASCAL`.
4	The word `NONCON` is required on the first reaction line if any of the reactions do not conserve the number of surface sites of a given type.
5	The reaction description can begin anywhere on this line. All blank spaces, except those separating the Arrhenius coefficients, are ignored.
6	Each reaction description must have `=`, `<=>`, or `=>` between the last reactant and the first product.
7	Each species in a reaction is described with a unique sequence of characters (name) as they appear in the species data and the thermodynamic data. However, if a species name is not unique (because it is duplicated in another phase), the name must be modified by appending its slash-delimited phase name: as `name` `/` `phase` `/`.
8	Stoichiometric coefficients are represented by an integer or real number preceding a species name. The default is to assume a stoichiometric coefficient of `1`. The "`#` " symbol preceding the stoichiometric coefficient denotes a coefficient which is additionally multiplied by a "`yield` " multiplier.
9	A reaction description may be contained on more than one line. If a line contains the symbol `&`, all information following the `&` symbol will be ignored and the next line will be considered a continuation of the first.
10	Three Arrhenius coefficients must appear in order (, , and ) on each Reaction line, separated from each other and from the reaction description by at least one blank space; no blanks are allowed within a number.
11	There cannot be more than six reactants or six products in a reaction.
12	To specify a sticking coefficient rather than a rate constant the three numbers after the reaction description have the meaning , , and (see Equation 4–10 of the Chemkin Theory Manual ) and the auxiliary reaction data word `STICK` must appear on the next line of input. To use this option the reaction must have only one gas-phase species as a reactant and its stoichiometric coefficient must be `1`.
13	All characters on a line following an exclamation mark are comments.
14	For best results, an `END` statement should follow reaction input.

4.5.2.1. Vapor-Liquid Phase Transfer

For liquid species to participate in the vapor-liquid phase transfer process, they must be mapped one-to-one. This mapping is provided in the form of a unimolecular reaction, as shown in Figure 4.6: Examples of Reaction Data for Liquid Phase . Each reaction must be followed by the auxiliary data line VLE. The model for handling the vapor-liquid equilibrium (VLE) levels is defined by the keyword IDEAL or HENRY on the same line. Additional auxiliary inputs are described next. The three parameters specified as the reaction rate coefficients follow the Arrhenius form. However, they are used as a multiplier to the actual rate of mass transfer between the phases. We recommend using the value of 1.0 0.0 0.

Figure 4.6: Examples of Reaction Data for Liquid Phase

REACTION
nc12h26(l) = c6h12-1(l) + nc6h14(l)                  5.4E+13  0  57907. !volumetric reaction in liquid bulk
! Vapor Liquid transfer steps - must have one species from liquid and gas on either side of the reaction step.
!    Keyword VLE provides equilibrium model; KMASS can be used to explicitly provide mass transfer rate constant.
!    Rates of phase change are controlled by mass transfer models in Chemkin reactor.
nc12h26(l) = nc12h26    1.0  0.0  0.   !Mass transfer rate multiplier
  VLE / IDEAL/                         !IDEAL = Raoult's law, HENRY = Henry’s law
nc6h14(l) = nc6h14      1.0  0.0  0.
  VLE / IDEAL/                  
c6h12-1(l) = c6h12-1    1.0  0.0  0.
  VLE / IDEAL/                  
END