Conceptual Models > Database selection and modification

Setting the activity model to ideal solution

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ahmadreza_shojaee:
Dear all,

Is there anyway that I can set the activity coefficient model to the ideal model (equals to molality)?

Kind regards,
Ahmad 

dlparkhurst:
Not easily.

For an ion-association model like phreeqc.dat, you will have to use SOLUTION_SPECIES and redefine -gamma for each species with a large dh_a (for ions) and 0 for dh_b. For example,


--- Code: ---SOLUTION_SPECIES
Cl- = Cl-
-gamma 1e6 0

--- End code ---

ahmadreza_shojaee:
Thank you very much, David.

One more question about Debye-Huckel a and b parameters. Are these parameters exact values for each specie, or they could be a range?

Kind regards,
Ahmad

dlparkhurst:
The a and b parameters are usually fit to empirical data, so the values for a single species may vary depending on the data that are fit.

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