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Geochemist's Workbench Support Forum

SnI2 vs SnI4 : formation constant?


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Hi Jaehyuk,

The GWB is primarily a suite of programs that utilize equilibrium constants. As an example, using an internal dataset of equilibrium constants for independent reactions plus user-supplied data, like concentration, pH, and T, it can calculate the distribution of species in a system at equilibrium.

One of the programs, Rxn, can be used to calculate equilibrium constants specific to the reaction that you specify. For example, in thermo_minteq.tdat, you can find a reaction SnNO3+ + 2 H2O = Sn(OH)2 + 2 H+ + NO3-, with a log K of -7.94 at 25 C. You can also find the reaction Sn++ + 2 H2O = Sn(OH)2 + 2 H+ in the dataset, with a log K of -7.094 at 25 C. The reaction SnNO3+ = NO3- + Sn++ isn’t found in the dataset, but with program Rxn, a user could form that reaction and calculate the equilibrium constant (log K -0.8460) by combining the first two reactions.

I’m assuming you’re looking for the equilibrium constant for a reaction like SnI4 = Sn++++ + I-. As I mentioned before, there is no form of this reaction included in any of the datasets that we distribute. You’ll have to search the literature or perform an experiment to find that equilibrium constant. Once you do find it, it’s a simple matter to add it to a GWB thermo dataset. Once it’s in the dataset, you can incorporate that reaction in a variety of geochemical calculations.


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