Questions on aqueous kinetics, Sample Problem 10.

Hello everybody,

I have some questions concerning the representation of aqueous kinetics reactions and especially the sample problem 10 from the Toughreact V3-OMP description.

1) In table 1.10-2 (p. 75 in the pdf) the value for V_m^Fe is given as 15.0e-12, while in the example of the chemical.inp file (p. 80) it is written as 3.0e-12. Does anybody know which one is correct?

2) The units for the Vm rate constant values in that particular table are specified as s^-1, while in the input file they are denoted as mol/kg*s, which should make more sense from my point of view. Which one is correct?

3) At a different example (no. 9, p. 67), the unit for the rate constant is given as mass/L*s, but how is (or can be) this related to reactions where different chemical species are produced?

4) I tried to use aqueous kinetics for the oxidation of SO2(aq) to SO4-2 and added the following input:

x  I tried to include the affinity term (fG) as shown, but the simulation does not work. If I exclude the specific part in record Akin-4, the simulation runs. Has anybody had similar problems?

5) The value 31.076 in record Akin-4 is the log of the equilibrium constant for that reaction calculated from the regression coefficients from the data base at the prevailing temperature of 66°C. Although my actual simulation is isothermally treated, how could the K value be included for varying temperatures? Or is this value limited to a temperature-independent treatment?

Any comments are kindly appreciated!

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  • One addendum: If I artificially change the value for the equilibrium constant from 31.076 to 2.0 or smaller, then the simulation runs. At values between 2.0 and 25.0, it theoretically runs, too, but it reduces time step size to the order of dt=E-04s.

  • The answer to my question 4 is as follows. In the Toughreact V3-OMP manual - Draft (p. 37) the listing sequence is

    • irkaq_typ, rkaq_logK, rkaq_cf (which is correct), but the sequence of explanation is
    • irkaq_typ, rkaq_cf, rkaq_logK

    So the manual is misleading at this part of description from my point of view.

    Any ideas concerning the other questions?

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