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.
Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.
The URL of this page is:
Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
Visitor number 2591 since Jan 22, 1998.