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Rate Units of Custom Rate Law for Redox Reaction

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I'm attempting to use a custom rate law for a redox reaction but first trying to convince myself I understand the units expected by GWB in the value I return at the end of the custom rate law script (which is included as part of the GWB script using the requisite curly braces). The full script is attached.


I'm looking at a (made up) reaction that is 2nd order in one reactant and 1st order in another reactant. I'm using the pre-exp and act_en variables to calculate the constant as a function of temperature (rather than setting the rate constant directly). I use the same equation as the built in rate law for redox reactions, the goal being to reproduce the built-in rate law to make sure I understand what units the returned value need to have in potentially more complicated future custom rate laws.


Assuming my pre-exp factor is entered with the correct units, (mol/kg)^-2 s^-1, for the reaction I describe (in which I use concentrations for the promoting species), then my understanding is the returned rate should be in mol/kg/s, but the value I print out within the script does not match the value in the output file for a given Step #. I also tried multiplying the value by Wmass and comparing to dndt (also printed out within the custom script). Again, no match. I even tried setting theta to 0 and comparing the calculated value to dndt0 thinking perhaps it was a matter of weighting, but by the end of a step, there is still no match. The differences are not huge, so maybe I'm unnecessarily concerned, but it's making me wonder whether I'm giving GWB the quantity it is expecting.


So, my questions are:


1. What units should be returned for a rate at the end of a custom rate law for a redox reaction if not mol/kg/s?

2. How is this value used by React, that is, does it use the returned rate to integrate over the time step to then calculate the change in concentration of a kinetic reactant over that interval?

3. If I'm understanding correctly, why can't I get the calculated rate to match either the rate shown in the output file or the rate carried by React's memory (dndt) after multiplying by Wmass?

4. If I'm not understanding, what am I missing?




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