Thank you for bringing the discrepancy about O2(g) to my attention. Your analysis is correct, although mixing values from different databases is probably the type of thing that caused the problem in the minteq data base. The delta H for O2(g) in the minteq data base appears to be a poor selection or an error. The phreeqc.dat delta H gives the correct tendency for solubility. However, to confuse things more, I think the value in llnl.dat (delta H = -2.9 kcal; -12.1336 kJ) gives a better fit to solubility measurements. I am reluctant to change minteq.dat in the distribution of PHREEQC. I checked and the data in minteq.dat are consistent with the database for the MINTEQ program, so PHREEQC results with minteq.dat should be consistent with results from the program MINTEQ. I am not going to attempt to analyze all the thermodynamic data, it is just too big a task. I am reasonably confident of the basic data in phreeqc.dat and wateq4f.dat. Also, the data in llnl.dat has probably been through more rigorous analysis than the other databases. In general, I am somewhat suspicious of minteq.dat, just because I found many errors in stoichiometry when I was translating the data to make minteq.dat, but I made no attempt to evaluate the log K's and delta H's. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled "Kaoru Masuda" <k-masuda@xxxxxxxxxxx To: "David L Parkhurst" <dlpark@xxxxxxxx> elco.co.jp> cc: In-Reply-To: <002701c253ca$4f6f7940$033a310a@xxxxxxxxxxxxxxxxxxxxx> Subject: O2(g) Minteq 09/03/02 10:19 PM Dear Dr. Parkhurst, I am one of the PHREEQCI users. I think I found some discrepancy on deltaH of O2(g) dissolution. When I tried to calculate O2 solubility in water at different temperatures using Minteq.dat that is bundled with PHREEQCI. (I usually use Minteq.dat because it contains a lot of data for solutility products.) For example, when I set the partial pressure logP=-2, calculated concentrations of O2 in the solution are 2.19E-5 mol/L at 25C 2.37E-5 mol/L at 40C On the other hand, using PHREEQC.dat, 2.19E-5 mol/L at 25C 1.89E-5 mol/L at 40C My understanding is that gas solubility decrease at higher temperature. O2 gas data in Minteq.dat and Phreeqc.dat are followings. Minteq.dat O2 + 4H+ + 4e- = 2H2O logk1 = 83.12 delta_H1=-133.83 Phreeqc.dat O2 = O2 logk2 = -2.96 delta_H2=-1.844 I think the data in Minteq is the combination of Henry's constant and dissociation constant of H2O; 2H2O = O2 + 4H+ + 4e- logk3 = -86.08 delta_H3=134.79 and relationship between logk1,k2,k3 is logk1=logk2 - logk3. I think this is the same for delta_H and delta_H1=delta_H2 - delta_H3. If it's true, deta_H1 should be -136.634 If I replaced O2(g) data in Minteq.dat by O2 = O2 logk= -2.96 delta_H2=-1.844 or I replaced delta_H by -136.634 , calculation results were same as those by Phreeqc.dat. I will appologize if I am wrong or this problem is already known. Best regards, Kaoru Masuda, Kobe Steel, Ltd.
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