Creating thermodynamic databases

[JMCarmona10]

Description

Hello, Allan

I have a question about measuring how the initial concentration of a species changes compared to its equilibrium concentration after a reaction finishes. I created a thermodynamic database with two phases - aqueous and solid - and included 8 reactions, none involving gases. However, when I try to determine how the initial concentrations change over the course of the reaction to reach equilibrium, the concentrations remain unchanged. I realized that with the reactions I defined, I can only calculate equilibrium concentrations for the products formed, not observe how the concentrations of all species change over time to reach equilibrium.

Example

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What is your operating system?

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Additional Information

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[allanleal]

Hi Manuel, thanks for your question. It’s very difficult to know what is going on without a reproducible example (one that is simple and to the point). Would you be able to provide it?

[JMCarmona10]

I am writing with a question about creating thermodynamic databases. Specifically, I would like to know if there is a way to fix the equilibrium constants for a reaction at different temperatures within the software.

I have calculated equilibrium values for my reaction across a temperature range. However, I want to understand how valid these values are based on the models and data in the software.

[allanleal]

Do you mean providing logK data for interpolation? This is currently not supported. Only standard Gibbs energies and other standard-state properties can be provided for interpolation (as shown in the link below for species Ca+2).

https://reaktoro.org/tutorials/advanced/creating-custom-databases.html?highlight=interpolation#a-more-complicated-custom-thermodynamic-database-in-yaml-format

[JMCarmona10]

Rather than interpolating logK values, im tryingto use experimental values at different temperatures. For example, the following two reactions had logK values that varied with temperature in the experiment. Im trying to create a database close to the experiment environment as close as possible. And then run the chemical equilibrium.

I came across some code that assigns logK values to different chemical reactions. I'm wondering if it would be possible to modify the code to specify logK values for individual reactions at different temperatures.

[allanleal]

OK, try the following. First, you define a function model (any name possible) that returns a ReactionStandardThermoProps object (consult https://reaktoro.org/api).

def model(args):
    T = args.T  # temperature in K
    P = args.P  # pressure in Pa
    logK = 1.23 + 2.34/T - 3.45e-3*T  # compute log(K) for current T
    lnK = logK * math.log(10)  # convert log(K) to ln(K)
    
    rprops = rkt.ReactionStandardThermoProps()
    rprops.dG0 = -R*T*lnK  # compute dG0 for the reaction using lnK

    return rprops

Then, maybe, you may have to convert it to ReactionStandardThermoModel as follows:

model = rkt.ReactionStandardThermoModel(model)  # create a reaction model

Now, instead of using .withEquilibriumConstant in the screenshot, you use .withReactionStandardThermoModel(model).

You can do this for other reactions as well.

If you run into issues, please consider creating a very minimal script reproducing the problem and attach here.

[JMCarmona10]

Thank you i was able to write all my reactions and now it matches the chemical system of the experiment