using enthalpy of solution species (delta_h) in BASIC calculations

[francesco]

Greetings Phreeqc users/developers.
I was wondering if there is a specific statement for the BASIC interpreter that allowed to use the enthalpy of a solution species (delta_h) for further calculations.
I was consulting the manual but I found no information.

Many thanks!

Francesco Endrizzi, KIT-INE (DE)

[dlparkhurst]

No, sorry, there is not a Basic function for delta_h, only for log K: LK_SPECIES, LK_PHASE, LK_NAMED.

[sestes]

Hello All,

I too would like to call the enthalpy for a particular reaction with the BASIC Interpreter for further calculations. Any chance some work has been done since 2017 to add this feature?

Thanks,

Shanna

[dlparkhurst]

Sorry, no function for Delta H has been added.

(Note that Delta_H is not used to adjust the log K for temperature if an analytical expression is defined.)

[sestes]

Thank you for the quick reply. It's too bad that there is no enthalpy function for the BASIC Interpreter. I was hoping to couple PHREEQC output with PEST to optimize enthalpy values from calorimetry data. To do this, I need to calculate the cumulative heat (Q = n * delta_H) associated with each step in a titration, and it seemed like I would be able to do these simple calculations using BASIC and USER_PUNCH. Oh well, I will find another way.

Thanks!

[dlparkhurst]

I will add a couple new Basic functions to return the delta H of species and phases. The delta H will probably be done numerically based on the Van't Hoff equation at the temperature of the calculation to account for analytic expressions for log K.

We are working on a new release, but I can't promise when it will be done.

[sestes]

Great, thank you! I think this will be a useful feature for PHREEQC users. Will the new BASIC functions default to the database "delta_h" value when no analytic expression is available?

Also, my PEST expert colleague believes there is a workaround for calling enthalpy when the enthalpy is also a parameter that will be optimized. Once we have a working solution, I will post the code here for others to use.

:-)

[dlparkhurst]

I wrote two functions DELTA_H_SPECIES(species name) and DELTA_H_PHASE(phase name). They numerically evaluate the delta H. if an analytical expression exists, the result will be at the temperature of the calculation. If no analytical expression exists, the numerical result should be equal to the delta H specified in SOLUTION_SPECIES or PHASES.

Note you can define SOLUTION_SPECIES and PHASES within the input file (which will override the database). That should make it relatively easy to include as a parameter for PEST.

[sestes]

Excellent, this is perfect. Thank you! I look forward to the update.