           Description of Thermodynamic Database Files
                         (DATABASE.TXT)
                               for

                            MINTEQA2

                          Version 3.11

                         December 1991


         Center for Exposure Assessment Modeling (CEAM)
              U.S. Environmental Protection Agency
               Office of Research and Development
                Environmental Research Laboratory
                      College Station Road
                   Athens, Georgia  30613-0801

                 (404) 546-3549 / (FTS) 250-3549



Introduction
------------

The following is an explanation of MINTEQA2's thermodynamic 
database files.  This information is useful for adding new 
reactions to any of the 4 database files: THERMO.DBS, TYPE6.DBS, 
REDOX.DBS or GASES.DBS.  Before attempting to add to or modify 
these files, note the following:

o The user should make a backup copy of the file to modify before
  starting.  Give the copy a name such as TYPE6.SAV.  This is just
  in case things don't go as planned.

                Example: COPY TYPE6.DBS TYPE6.SAV

o When adding to or modifying the thermodynamic database, if the
  reaction is an AQUEOUS species, only edit the file THERMO.DBS.  
  If the reaction is a SOLID (mineral), REDOX couple, or GAS, 
  the user must edit two files as explained below.  The main file, 
  THERMO.DBS, is divided into several sections delineated by 
  blank lines and lines that contain a zero in column 7.  The 
  first section is for AQUEOUS species and is followed by 3 lines 
  with zeroes separated by blank lines.  After these separator 
  lines, the next section is for SOLIDS and that section is 
  followed with one blank line and one line with a zero.  The 
  next section is for REDOX couples and is followed immediately 
  by the GAS section.  The file is terminated with a blank line 
  then a line with a zero.  YOU MUST HONOR THE SECTIONAL 
  DIVISIONS WHEN MAKING ADDITIONS--DON'T DELETE OR CHANGE THE 
  SEPARATOR LINES.  The arrangement of these sections serves to 
  signal MINTEQA2 as to the nature of the species (AQUEOUS 
  species, SOLID, etc.). 

o To add a new AQUEOUS species, it need only be entered in
  THERMO.DBS.  The other files remain unchanged.  
                                                            
o To add a new SOLID (MINERAL), it must be entered in THERMO.DBS
  and in TYPE6.DBS.
    
o To add a new REDOX couple, it must be entered in THERMO.DBS
  and in REDOX.DBS.

o To add a new GAS, it must be entered in THERMO.DBS and in
  GASES.DBS.

o After all desired changes are made to THERMO.DBS, new versions of 
  the corresponding files that are actually used by MINTEQA2 and 
  PRODEFA2 must be created.  This is easily accomplished by executing
  the program UNFRMT.EXE (included on the distribution media).  Before
  executing UNFRMT, rename the current THERMO.UNF and TYPE6.UNF files
  to something else for safe keeping.  UNFRMT will fail to execute if 
  files with these names exist.  UNFRMT creates unformatted versions
  of THERMO and TYPE6 that can be read faster by MINTEQA2 than can  
  their formatted counterparts.  The unformatted files cannot be 
  edited directly because they are unintelligible.  The program 
  FRMT.EXE does exactly the inverse of UNFRMT so that THERMO.DBS and
  TYPE6.DBS can be recreated from the unformatted files if desired.
  
o Constants for all entries are referenced to a temperature of
  25 degrees C.  AQUEOUS species constants are for ionic strength 
  of zero, REDOX couple constants are for zero potential, and GAS 
  constants are for a partial pressure of one atmosphere. 



Explanation of Entries in the Thermodynamic Database Files
THERMO.DBS, TYPE6.DBS, REDOX.DBS, and GASES.DBS  
----------------------------------------------------------

Each reaction is specified by a two or three line entry.  The 
explanation of each line is as follows:

---------------------------------------------------------------------
FIRST line -

Column(s)         Meaning                                   Format
---------------------------------------------------------------------
1 -  7      Species reaction product ID number.  If          I7
            the user is adding a new reaction, create this
            number. 

            For AQUEOUS and GAS species, the 7-digit ID  
            is formed from the 3-digit component ID # of 
            the major cation suffixed by the 3-digit 
            component ID # of the major anion suffixed
            by a single digit to ensure that the 
            resulting 7-digit number is unique within
            the entire database.

            For SOLID species, the 3-digit component   
            ID # of the major cation is prefixed with
            a 2-digit code that represents the class
            to which the solid belongs.  The 2-digit
            class codes are listed below.  The resulting
            5-digit number is suffixed with 2-digits to
            ensure that the final 7-digit number is 
            unique within the entire database.

               2-Digit Codes for Classes of Solids
            ------------------------------------------
              Code  Class                Code  Class
              00   Elemental             51   Nitrate
              10   Sulfide               52   Borate   
              11   Cyanide               60   Sulfate  
              12   Selenide              61   Selenite,Selenate 
              14   Antimonide            70   Phosphate   
              20   Oxide and Hydroxide   72   Arsenate     
              30   Multiple Oxide        73   Vanadate 
              40   Bromide               80   Orthosilicate   
              41   Chloride              82   Chain Silicate
              42   Fluoride              84   Framework Silicate
              43   Iodide                86   Sheet Silicate    
              50   Carbonate             
                                                
                                               
            ------------------------------------------


            For REDOX couples, the 3-digit component 
            ID # of one of the redoxing pair is
            prefixed by the other and the resulting
            6-digit number is suffixed by a single
            digit to ensure that the final 7-digit ID
            number is unique within the entire database.   
 
8           blank
        
9 - 20      Species reaction product name.  With only 12     A12
            spaces, it could be necessary to abbreviate.
            Subscripts aren't possible but do use parentheses
            where appropriate.  If the species is charged,
            always hang the charge on the end of the name
            prefixed with the appropriate algebraic sign.
            For SOLIDS, mineral names are preferred to
            chemical formula names. 

21 - 30     Enthalpy change, i.e., delta H for the           F10.4
            reaction (kcal/mole).  MINTEQA2 uses this 
            value to adjust the equilibrium constant for 
            temperatures other than 25 degrees C.

31 - 40     Log K.  Common logarithm of the equilibrium      F10.4
            constant for this reaction. 

            For AQUEOUS species, this is a thermodynamic 
            stability or formation constant, i.e., for 
            the reaction
                                    
                    wA + xB  <----->  yC + zD   ;
                                 
                                y    z
                             {C}  {D}
                     K =   _____________            
                                w    x
                             {A}  {B}
                                                            
            where brackets { } denote activity.
            For MINTEQA2, this reaction would be written  

                    wA + zB - yC  <----->  zD
    
            in the thermodynamic database where A, B, and
            C are MINTEQA2 components and D is an AQUEOUS
            species and is referred to here as the species
            reaction product.
                    
            For SOLIDS, K is the reciprocal (log K is the 
            negative) of the solubility product.  This is
            because MINTEQA2 treats precipitation reactions as if
            written with reactants on the left and precipitates 
            on the right that is reversed compared with the
            solubility product rule.  A representative MINTEQA2 
            precipitation reaction is

                   Ag+1  +  Cl-1  <----->  AgCl (s) ;

                                        
                                {AgCl}
                     K =    ______________            
                             {Ag+1} {Cl-1}
                                   

            where brackets { } again denote activity.  The
 
            activity of pure AgCl(s) is equal to unity by
            convention so,

                                       1
                           K =    _____________  
                                  {Ag+1} {Cl-1}


            Now, the solubility product rule applied to the
            silver chloride reaction gives

                          Ksp  =  {Ag+1} {Cl-1}.
            
            Therefore, the K needed in MINTEQA2 is related to the Ksp

                                     1
                          K   =   ________     or
                                    Ksp        

        
                          log K   =  -log Ksp .


            In summary, the log K value for a SOLID in the 
            database is the negative of log Ksp.

            For REDOX couples, the value entered for log K
            is computed from the Nernst equation

                           o     RT
                    E  =  E  -  ____  X  2.303 log Q
                                 nF                        

                                       o
            where E is the potential, E  is the standard 
            reduction potential at 25 degrees C, R is the molar
            gas constant, T is the absolute temperature, F is
            the Faraday constant, n is the number of electrons
            in the half-reaction, and Q is that function of
            concentrations (activities) of products and reactants 
            that occurs in the equilibrium constant that we seek. 
            For potentials measured in volts at 25 degrees C
   
                           o      0.05916
                    E  =  E   -  _________  log Q .
                                     n           

            Just as log K's for AQUEOUS species are referenced
            to an ionic strength of zero, the log K's for 
            REDOX couples are referenced to a potential of
            zero.  So, with rearrangement and taking E = 0,
            the above equation becomes
                                        o
                                     n E 
                         log K  =  _______
                                   0.05916
                                 
 	    where Q has been replaced by K denoting equilibrium.
            For the Fe(III)/Fe(II) couple (species ID # 2812800),
                                 _     
                    Fe(III)  +  e   ------>  Fe(II)

            for which the standard reduction potential is 0.771
            and n = 1, the above expression gives              

                         log Q  =  13.032.

            This is the value entered for log K in that reaction.   

            For GASES, the log K entered is log Kp where the
            partial pressure of the gas is in atmospheres.  The
            values currently in the database files are for a
            partial pressure of one atmosphere.  If the user wants
            to compute equilibria at pressures other than one atm,
            adjust the log Kp accordingly.  PRODEFA2 makes this
            adjustment automatically by inquiring the desired
            partial pressure, obtaining the constant for one atm 
            from the database, and entering the corrected log K
            in the input file.  An example of a gas reaction
            and the partial pressure adjustment is species
            3301403
                             
                   CO3-2  + 2H+1  -  H20  <----->  CO2 (g)

            The log Kp at one atm is 18.16.  The log of the partial 
            pressure of CO2 (g) in the atmosphere is about  -3.5.
            Therefore, the corrected log Kp' is

                                               -3.5
                    log Kp' =  log Kp -  log(10    )
                            =  18.16  -  (-3.5)
                            =  21.66 
                   
            MINTEQA2 requires that the partial pressures of all
            gases be fixed for a given problem.

41 - 48     Maximum reported log K.  This entry is made      F8.3
            only for SOLID species and is not actually
            used in MINTEQA2's equilibria calculations.
            It is intended to provide a means of judging 
            the reliability of the log K given in columns
            31 - 40.

49 - 56     Minimum reported log K.  This entry is made      F8.3
            for SOLID species only and is not actually
            used in MINTEQA2's equilibria calculations.
            It is intended to provide a means of judging 
            the reliability of the log K given in columns
            31 - 40.

57 - 61     Charge of species reaction product.              F5.2
   
 
62 - 66     Debye-Huckel "a" parameter for species reaction  F5.2
            product.

67 - 71     Debye-Huckel "b" parameter for species reaction  F5.2
            product.

72 - 80     Gram formula weight of species reaction          F9.4
            product.  No entry for REDOX couples.

---------------------------------------------------------------------
SECOND line -

Column(s)         Meaning                                   Format
---------------------------------------------------------------------

1 -  5      Carbonate alkalinity factor.  This entry is      F5.2
            made only for AQUEOUS species that have 
            carbonate (ID # 140) as a component.  In cases
            where the user has chosen to specify the 
            inorganic carbon as alkalinity (this is an option 
            when executing MINTEQA2), the carbonate alkalinity 
            factor is used to convert to total inorganic carbon
            (carbonate) concentration.

            To compute the carbonate alkalinity factor for a
            new species, use the formula:

            alkalinity factor = (2 x STOIC(CO3-2)) - STOIC(H+)

            where STOIC(CO3-2) is the stoichiometry of component
            ID # 140 (carbonate) and STOIC(H+) is the
            stoichiometry of component ID # 330 (hydrogen) in
            the reaction.

6           blank

7           Number of components (as reactants or            I1
            products) in this reaction.  Maximum = 9.

8  - 10     blank

11 - 17     Stoichiometry of the first component.            F7.3
            Negative if the component is a reaction product,
            that is, if it occurs in the left-hand side of 
            the chemical equation with a negative coefficient.          

18          blank
  
19 - 21     ID number of the first component.

22 - ?      Additional stoichiometry/component ID # pairs 
            with separating spaces so that the total 
            number of pairs is equal to the number of
            components as specified in column 7.  These 
            are entered in the same manner as the first
            pair in columns 8 - 21, that is, 3 blank
            columns followed by seven columns for the 
            stoichiometry in F7.3 format, one blank
            column and finally, three columns for the 
            component ID # in I3 format.  The remainder
            of the second line will hold 4 additional
            pairs through column 77.  If the total number 
            of components is greater than 5, continue on
            a third line with the 3 columns 78 - 80 of
            the second line counted as the 3 blank columns
            for the sixth pair.  Use columns 1 - 7 of the
            third line for the stoichiometry of the sixth
            pair.  Column 8 should be blank and columns
            9 - 10 should contain the component ID #. 
            Continue with the 3X,F7.3,1X,I3 format for
            up to three additional pairs on the third line.



Examples of Entries in the Thermodynamic Database
Files THERMO.DBS, GASES.DBS, REDOX.DBS and TYPE6.DBS               
----------------------------------------------------

     ****** Examples of AQUEOUS Species-

3300020 OH-         13.345    -13.998                    -1. 3.5  0.0  17.0074
      2     1.000   2    -1.000 330
1501401 CACO3 AQ    4.0300    3.1500                      0. 0.0  0.0  100.0890
 2.00 2     1.000 150     1.000 140
2113300 CR+3         -20.1400    9.62                   3.00 0.00 0.00  51.9960
 0.00 3     1.000 211     2.000 330    -2.000   2

     First reaction --
      Species ID number:  3300020           Minimum Log K:   not used
      Species name:       OH-               Species charge:  -1
      Delta H:            13.345 kcal/mol   Debye-Huckel A:   3.5
      Log K:             -13.998            Debye-Huckel B:   0 or unknown
      Maximum Log K:      not used          Gram Formula Wt.: 17.0074

      Alkalinity factor:  none              Number of components: 2
      Chemical Equation (from stoichiometry/components):

                        H2O   -   H+1   <----->   OH-
 
      or, in terms of (stoichiometry)component ID #'s:

                    1(002)  -  1(330)  <----->  3300020


     Second reaction --
      Species ID number:  1501401           Minimum Log K:   not used
      Species name:       CaCO3 (aq)        Species cha
      Species ID number:  1501401           Minimum Log K:   not used
      Species name:       CaCO3 (aq)        Species charge:   0
      Delta H:            4.03 kcal/mol     Debye-Huckel A:   0 or unknown
      Log K:              3.15              Debye-Huckel B:   0 or unknown
      Maximum Log K:      not used          Gram Formula Wt.: 100.089

      Alkalinity factor:  2.0               Number of components: 2
      Chemical Equation (from stoichiometry/components):

                      Ca  +  CO3-2  <----->  CaCO3

      or, in terms of (stoichiometry)component ID #'s:

                 1(150)  +  1(140)  <----->  1501401


     Third reaction --
      Species ID number:  2113300           Minimum Log K:   not used
      Species name:       Cr+3              Species charge:  +3 
      Delta H:           -20.140 kcal/mol   Debye-Huckel A:   0 or unknown
      Log K:              9.62              Debye-Huckel B:   0 or unknown
      Maximum Log K:      not used          Gram Formula Wt.: 51.996

      Alkalinity factor:  none              Number of components: 3
      Chemical Equation (from stoichiometry/components):

                  Cr(OH)2+  +  2H+1  - 2H2O  <----->  Cr+3

      or, in terms of (stoichiometry)component ID #'s:

               1(211)  +  2(330)  -  2(002)  <----->  2113300

            

     ****** Example of SOLID (Mineral)-

6010000 BARITE          -6.280     9.976    .000   9.773                233.4016
      2     1.000 100     1.000 732

      Species ID number:  6010000           Minimum Log K:    9.773
      Species name:       Barite            Species charge:   0
      Delta H:           -6.280 kcal/mol    Debye-Huckel A:   unknown
      Log K:              9.976             Debye-Huckel B:   unknown
      Maximum Log K:      unknown           Gram Formula Wt.: 233.4016

      Alkalinity factor:  none              Number of components: 2
      Chemical Equation (from stoichiometry/components):

                       Ba+2  +  SO4-2  <----->  BaSO4 (Barite)

      or, in terms of (stoichiometry)component ID #'s:

                    1(100)  +  1(732)  <----->  6010000



     ****** Example of a REDOX Couple

2812800 FE+3/FE+2   -10.0     13.032
      3     1.000 281    -1.000 280     1.000   1

      Species ID number:  2812800           Minimum Log K:   not used
      Species name:       Fe+3/Fe+2         Species charge:  not used
      Delta H:           -10.0 kcal/mol     Debye-Huckel A:  not used
      Log K:              13.032            Debye-Huckel B:  not used
      Maximum Log K:      not used          Gram Formula Wt.: not used

      Alkalinity factor:  none              Number of components: 3
      Chemical Equation (from stoichiometry/components):

               Fe+3  -  Fe+2  +  E-1  <----->  activity ratio of Fe+3/Fe+2

      or, in terms of (stoichiometry)component ID #'s:

        1(281)  -  1(280)  +  1(001)  <----->  2812800



     ****** Example of a GAS

3301403 CO2(GAS)    -0.53     18.16                                    41.0100
      3     1.000 140     2.000 330    -1.000   2
 
      Species ID number:  3301403           Minimum Log K:   not used
      Species name:       CO2 (g)           Species charge:   0
      Delta H:           -0.53              Debye-Huckel A:   unknown
      Log K:              18.16             Debye-Huckel B:   unknown
      Maximum Log K:      not used          Gram Formula Wt.: 41.010

      Alkalinity factor:  none              Number of components: 3
      Chemical Equation (from stoichiometry/components):

                   CO3-2  +  2H+1  -  H2O  <----->  CO2 (g) 

      or, in terms of (stoichiometry)component ID #'s:

             1(140)  +  2(330)  -  1(002)  <----->  3301403



                    #########################


JA/ja/dwd - September 1991 - E:\MINTEQA2\DATABASE.TXT
