clarification on PorousFlowAqueousPreDisChemistry

[navier-rgb]

Hello,
Could anyone please offer clarification on the following lines of code from PorousFlowAqueousPreDisChemistry?

https://github.com/idaholab/moose/blob/838e1c63f9aa3f6520da6639a2c8842eaf5366c3/modules/porous_flow/src/materials/PorousFlowAqueousPreDisChemistry.C#L350C4-L368C6

How did PorousFlow compute the "bounded" _reaction_rate[_qp][r]? Is it a derivative of some equation? Thank you.

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@GiudGiud @cpgr

[GiudGiud]

It s computed in that material. Seemingly the rate is simply back-computed from the change in another quantity. This expression also implicity assumes a 1st order scheme

[cpgr]

I think it does a logic check to see if the concentration after the reaction would be outside the physical range [0,1], given the timestep size and computed reaction rate. It the back-calculates a reaction rate to limit the concentration to these bounds, as @GiudGiud said.