The fugacity of H2O in aqueous phase

[Christinali91]

Hi David,

I am working on a CO2 solubility problem. I use 10^SI(CO2(g)) to get CO2 fugacity in the aqueous phase from Phreeqc. I wonder if it is correct to use a similar approach with H2O(e.g. 10^SI(H2O(g))) to get H2O fugacity in the aqueous phase.

Thanks so much for your help!

Best,
Christina

[dlparkhurst]

10^SI("H2O(g)") will give you the fugacity of water vapor in a gas phase that is in equilibrium with a solution. Activity of CO2(aq) is ACT("CO2") (or ACT("H2CO3") depending on the database.

The fugacity of H2O(aq) is equal to the activity of water--ACT("H2O") or 10^LA("H2O").

The two H2O fugacities (at GAS_PHASE equilibrium) are related by the Henry's law constant given by 10^LK_PHASE("H2O(g)").