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Adding a redox species (s0) to the database


AlisonK
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Hello,

I am using the LLNL thermodynamic database and attempting to add a new species under the redox species. Specifically I'd like to add zero-valent aqueous sulfur, which I am calling Szero.

 

When I add this, and attempt to open the database in Rxn, I receive the following error message: "mole wt. for Szero is bad (read_data). Expected = 32.066 Calculated = -31.932"

 

I did make sure to increase the number of redox species in the database by one, and have tried different names for the new species, different placement in the list of redox species, etc.

 

Here are the lines I have added to the database:

 

Szero

charge= 0.0 ion size= 4.0 A mole wt.= 32.066 g

4 species in reaction

-3.5000 O2(aq) -1.0000 H2O 2.0000 H+

1.0000 SO4--

500.0000 133.5394 500.0000 500.0000

500.0000 500.0000 500.0000 500.0000

* gflag = 1 [reported delG0f used]

* extrapolation algorithm: supcrt92 [92joh/oel]

* reference-state data source = 2011couture

* delG0f = -124.900 kcal/mol

* delH0f = -155.000 kcal/mol

* S0PrTr = 16.000 cal/(mol*K)

 

Note that the log K value is not correct; it's a placeholder for now. But I don't think that's the source of my problem. Any help anyone has would be deeply appreciated!

Alison

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I fixed it but have no idea why this worked. Basically I changed it so that instead of forming Szero from SO4--, I am forming it from HS-. This works! BUT WHY?

 

Szero

charge= 0.0 ion size= 4.0 A mole wt.= 32.066 g

4 species in reaction

0.5000 O2(aq) -1.0000 H2O 1.0000 H+

1.0000 HS-

500.0000 -38.4300 500.0000 500.0000

500.0000 500.0000 500.0000 500.0000

* gflag = 1 [reported delG0f used]

* extrapolation algorithm: supcrt92 [92joh/oel]

* reference-state data source = 2011couture

* delG0f = -124.900 kcal/mol

* delH0f = -155.000 kcal/mol

* S0PrTr = 16.000 cal/(mol*K)

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Hi Alison,

 

I moved your post to the main GWB page (you posted to the archive of old posts, so I didn't see it right away).

 

As for your question, your reaction for Szero written in terms of SO4-- is not balanced. Instead of -3.5 O2, it should read -1.5 O2 (Szero + H2O + 1.5 O2(aq) = 2 H+ + SO4--). The reaction written in terms of HS- was balanced properly, so it works just fine. Note that writing the reaction in terms of basis species SO4-- or redox species HS- is fine (just make sure the logK is correct), as long as HS- has been defined already in the redox species section.

 

Hope this helps,

Brian Farrell

Aqueous Solutions LLC

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