eh pH Diagram Help

[AshleyB]

Hello,

I was trying to make a redox diagram for NO3 with 12 samples I have input into GSS. I have watched the video tutorial and was unsure what the activity should be and how they knew what values to put in. Clarification on what the activity value refers to would be appreciated. I am unsure if it is a standard value for each element (Ex: SeO3 is always 1.0e-6 and U++++ is always 10.0) or if it changes.

Thanks,

Ashley

[Jia Wang]

Hello,

Act2 is used to calculate and plot Activity diagrams, which is a class of diagrams that show the stability of minerals and the predominance of aqueous species in chemical systems. An activity of a species is its effective concentration, given as the product of the concentration of species in molal times its activity coefficient. There is not a standard value for each species since the activity coefficient can vary depending on the condition of your system. If you have complete fluid analysis, you can use the SpecE8 application to calculate an activity of nitrate for your diagram in Act2. For more information on activity coefficients and model types, please refer to section 7 SpecE8 in the GWB Essentials guide. If you are interested in a more detailed explanation on activity coefficients, please see Chapter 8 Activity Coefficients in Craig Bethke's Geochemical and Biogeochemical Reaction Modeling text.

You can also refer Chapter 5 of the GWB Essentials User Guide for more examples in Act2. 

Hope this helps,
Jia Wang
Aqueous Solutions LLC