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How extrapolate thermodynamic equilibrium constants at only one temperature to other temperatures


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It is a simple question.
We want to calculate the dissolution and precipitation of Greenalite at 80℃ by X1t and React, but we have only the thermo data and LogKs at 25℃ from the previous thesis. (Log Ks=27.6)Is there a method to calculate or extrapolate LogKs at 80℃ from only 25℃ data
We attach the data and the link of previous thesis.

Thank you

https://pubs.geoscienceworld.org/gsa/gsabulletin/article/128/3-4/511/126243/An-authigenic-origin-for-Precambrian-greenalite

thermo(F-S-H) (1).tdat

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Hello,

I don't have access to the paper linked, but if you have other information such as the standard change in enthalpy for the reaction, you can calculate the equilibrium constant at another temperature using the Van't Hoff equation.

The GWB apps also is able to extrapolate using an internal polynomial expansion. For more information on the extrapolate feature, see the GWB Command Reference. The option to enable is located in the Stepping dialog in React and X1t. For more information on extrapolate, see the GWB Reference Manual. In general, I would advise caution when extrapolating log K's for temperature beyond the range of validity prescribed for the reaction of interest. The further you extrapolate outside the range prescribed, the less accurate the values may become. 

Hope this helps,
Jia Wang
 

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Hello,

A few clarifications to follow up.. Please take a look at the Options dialog for extrapolate instead of the Stepping dialog. That was a mistake on my part. 

If you are using the Van't Hoff equation, please consult a standard thermodynamic text to check. If the dataset only has one equilibrium constant at 25C, the extrapolation will only hold the value constant at a different temperature. You can find more details regarding the extrapolate command for React and X1t in section 6.35 and 8.39 respectively. 

By the way, the dataset you attached have equilibrium constants for greenalite at principal temperatures up to 150C. Perhaps this not the dataset in your description? If you want to run a simulation with attached dataset at 80C, the GWB will perform an interpolation to internally calculate the equilibrium constant at 80C. 

Best regards,
Jia 

 

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