[OLD] Organic ligand

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From: Kevin Telmer

Subject: Organic Ligand

I am interested in adding an organic ligand to the thermodynamic database ustilized by GWB (Thermo.dat). I would like to express it simply as R for starters and then model its interactions with Fe. The actual mollecule is C23N6O8H40 I thought about adding a species to Thermo.dat as follows:

RFe+

charge= 1.0 ion size= 20.0 A mole wt.= 528.3 g

2 species in reaction

1.000 R-- 1.000 Fe+++

12.65 13.08

Questions:

1. How do I add R to the basis species? Do I need to add it as an element? Is it better to add it to the aqueous species section of Thermo.dat as the mollecule itself?

2. I have only log K values for temperatures of 0 and 25C. Is there a problem if I do not include the other 6 temperatures?

 

From: Craig Bethke

Subject: Re: Organic Ligand

You can add the ligand as a basis species or -- if you know its stability relative to carbonate -- as a redox couple. You don't need to add it to the element or aqueous species lists. Add the ferric complex as an aqueous species. If you don't know the log K at a principal temperature, enter a value of 500. There's lots of information about modifying the thermo data in Appendix 3 ("Thermo Datasets") of the User's Guide.