shensel Posted December 14, 2020 Share Posted December 14, 2020 Hello, I am looking to add a number of basis species to thermo.com.V8.R6 and am confused by the ion size parameter. From what I gathered from reading the GWB reference docs, it is not the ionic radius? For example, bellow are a couple reactions I am trying to add, with the new species in bold: Mo+3 + 2H2O <--> MoO2+ + 4H+ + 2e- Log K = 9.96 MoO2+ + 2H2O <--> HMoO4- + 3H+ + e- Log K = 15.97 I've attached my database and the source pdf for the reactions (table 3). How can I find the ion size? Thanks, Scott Vlek and Lindsay (1977)_Molybdenum in Soils.pdf thermo.com.V8.R6+_Scotts dataset.tdat Quote Link to comment Share on other sites More sharing options...
Jia Wang Posted February 2, 2021 Share Posted February 2, 2021 Hello Scott, I am sorry I missed your post from earlier. To answer your question, you are right that the ion size parameter does not reflect the ionic radius of the ion. In practice, this parameter is obtained by fitting the Debye-Huckel equation to experimental data to account for effects such as hydration sphere surrounding the ion of interest. These values may differ between datasets and whether or not the activity model is using the classic Debye Huckel equation or B-dot model (extension of the classic D-H equation). At moderate ionic strength, the affect of different ion size parameter is relatively small compared to ion charge and other uncertainties. If you would like to read about the theory, a good place to look would be Jacob Kielland's publication for ion activity coefficients. He reports the results for common ion size parameter calculated for the Debye-Huckel equation. By the way, the best place to post a new topic is on the GWB forum front page. We aren't notified when new topics are posted in the archive section. The archive section is a great resource for looking at previous user questions and corresponding answers. Best regards, Jia Wang Quote Link to comment Share on other sites More sharing options...
shensel Posted February 7, 2021 Author Share Posted February 7, 2021 Thanks this helps a lot! And no worries, I will post on the front page from now on. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.