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Setting the activity model to ideal solution
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Topic: Setting the activity model to ideal solution (Read 136 times)
ahmadreza_shojaee
Top Contributor
Posts: 25
Setting the activity model to ideal solution
«
on:
August 09, 2024, 11:44:44 AM »
Dear all,
Is there anyway that I can set the activity coefficient model to the ideal model (equals to molality)?
Kind regards,
Ahmad
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dlparkhurst
Top Contributor
Posts: 3682
Re: Setting the activity model to ideal solution
«
Reply #1 on:
August 09, 2024, 02:55:55 PM »
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:
[Select]
SOLUTION_SPECIES
Cl- = Cl-
-gamma 1e6 0
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ahmadreza_shojaee
Top Contributor
Posts: 25
Re: Setting the activity model to ideal solution
«
Reply #2 on:
August 09, 2024, 07:52:59 PM »
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
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dlparkhurst
Top Contributor
Posts: 3682
Re: Setting the activity model to ideal solution
«
Reply #3 on:
August 09, 2024, 09:19:47 PM »
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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PhreeqcUsers Discussion Forum
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Conceptual Models
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Database selection and modification
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Setting the activity model to ideal solution