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Act2 crashes while using a modified thermo.dat


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I am trying to plot Eh-pH diagram for Au-CN system. There is no CN- in thermo.dat and hence added CN- among the redox couple species. But as soon as I direct Act2 to the new dat file, it crashes saying "Exit: Act2 stop:bad thermo database. Act2 is ending".Am I adding the data wrong? I have sent the modified thermo.dat file to support@gwb.com. Could you please advise?


Thanks & regards,


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Hi Suma,


It looks like you took the reaction for CN- from thermo.com.v8.r6+.dat and added it to thermo.dat. The problem is that the two databases differ in their choice of basis species for the nitrogen component. thermo.com.v8.r6+.dat uses NH3(aq), but thermo.dat uses NO3-. If you want to add CN- to thermo.dat, you'll need to write the reaction in terms of NO3-. Add the first two reactions together to get the third, which is what you want.


CN- + 2 H2O + .5 O2(aq) = HCO3- + NH3(aq) (Log K at 25 °C = 56.0505)

NH3(aq) + 2 O2(aq) = NO3- + H+ + H2O (Log K at 25 °C = 62.1001)


CN- + H2O + 2.5 O2(aq) = NO3- + HCO3- + H+ (Log K at 25 °C = 118.1506)


You can quickly accomplish this using Rxn with thermo.com.v8.r6+.dat. Just write the reaction for CN-, swapping NO3- in for NH3(aq).


By going to Run - Block - Append, then Run - Go, Rxn will copy to the clipboard the reaction and thermo data in a block of text that you can paste directly into thermo.dat.


One more thing, be sure to update the redox couples counter from 48 to 49.


Hope this helps,


Brian Farrell

Aqueous Solutions LLC

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