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Output change of enthalpy via BASIC

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Yongqiang:
Hi there,

I am trying to output change of enthalpy during feldspar dissolution. Is there a function for this parameter in PHREEQC?

Thanks,

dlparkhurst:
Sorry, that is not a capability of PHREEQC.

There are two Basic functions--DELTA_H_PHASE and DELTA_H_SPECIES--that return the enthalpy of reaction, in KJ/mol, at the given conditions. The enthalpy of reaction is calculated by differentiating the log K with respect to temperature.

Yongqiang:
Thanks, David!
I checked the manual. It seems that the manual is not the updated version to include above two functions.
I am confused about the unit of KJ/mol. If take the following reaction for an example, the KJ/mol refers to the enthalpy change of 1 mol KAlSi3O8 reacted?


K-feldspar
   KAlSi3O8 + 8 H2O = K+ + Al(OH)4- + 3 H4SiO4
   -log_k -20.573
   -delta_h 30.82 kcal
   -Vm 108.15

Thanks a lot!

dlparkhurst:
Yeah, the updated documentation is a little hard to find. The Help->Phreeqc User's Guide in PhreeqcI has the updated documentation. Also from the GitHub site, there is HTML at the following location.

https://github.com/usgs-coupled/phreeqc3/tree/master/HTMLversion/HTML

Yes, per mole of reaction.

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