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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