About setting details of chemical reaction rate in mfix

In the reaction of silane cracking, it can be seen that parameters such as silane diffusion rate, silane gas constant, membrane diffusion resistance, hydrogen adhesion constant and silane adhesion constant are set in the document usr_rates_des.f.
If I need to write a reaction code myself, how can I determine which parameters I need to define to ensure the completion of a chemical reaction? I don’t know how to do it.

You would typically get the details about a reaction mechanism from a published reference (journal article, book etc.). Then you will have to convert that information into code.