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Plotting Reaction Free Energy versus System Parameter

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I would like to know if it is possible to plot reaction free energy as a function of a system parameter, such as oxygen fugacity. For example, I am using Rxn to calculate the free energy of the reaction: H2(aq)  + .5 O2(g)  = H2O at a specified temperature, pH, reactant activities, and ionic strength. Running the program, I obtain a reaction free energy once I have specified all the parameters. However, I would like to see how the reaction free energy changes as I slide the oxygen fugacity. I tried using React to plot reaction free energy versus sliding oxygen fugacity, but I could not find a parameter for reaction free energy. Is it possible to use GWB to generate a plot as I have described?

Thanks in advance,


Hydrogen Oxidation.rxn

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Hello Jamison,

Thanks for attaching your Rxn file. The React application doesn't report information regarding the Gibbs free energy for a specific reaction in the way you have described. You can, however, quickly export the log activity or fugacity of each species needed to calculate the delta G for the reaction of interest. To do so, you would need to select the species activity (or gas fugacity) to plot and then go to Edit-> Copy as -> spreadsheet and paste the data into Excel.  As you may have discovered already, you can retrieve the log equilibrium constant value at any temperature (within the range prescribed by the thermodynamic data) using Rxn, which can then be used the delta G standard at the temperature desired.

If you want to do a simple calculation where the only changing value is your log fugacity of O2(g), then it might be easier to set up an equation in Excel and calculate delta G given the information known about your system.

Best regards,
Jia Wang
Aqueous Solutions LLC

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