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SELECTED_OUTPUT

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ehsan:
Hi
How to get activity coefficient carbon dioxide(aq) and water of the user_punch in SELECTED_OUTPUT?

dlparkhurst:
USER_PUNCH.

ehsan:

--- Code: ---     SELECTED_OUTPUT ; -file  output; -reset  false; -ionic_strength  false
     USER_PUNCH
     10 s$ = s$  + STR$(GAMMA("HCO3-")) + STR$(ACT("H2O"))
     20 PUNCH s$
--- End code ---
I used of ACT for activity coefficient of water and GAMMA for CO2 activity coefficient.
because GAMMA don't work for H2O
 

dlparkhurst:
Yes, the activity of water does not use the same approach of gamma * molality as all other aqueous species. Solvent water activity is essentially the mole fraction of water in the solution and the gamma is meaningless and set to 1 for ion association models.

For Pitzer and SIT databases, the osmotic coefficient is calculated and the activity of water is related to it by the relation, where mi is molality of the ith aqueous species and Mw is 18 g/mol:

ln(aw) = -(Σ mi ϕ Mw /1000)

ehsan:
Thanks David
I use the Phreeqc database to model a mixture of CO2 brine and I need to get the solution(brine) activity coefficient and the CO2 activity coefficient from the Phreeqc output.
And I don't know how to do that.
Do i use GAMMA(HCO3-) or GAMMA(CO2) for CO2 activity coefficient, GAMMA(H2O) or GAMMA(H+) for solution?

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