I want to learn how to create UDF file for CFDs Fluent. I don't know how and what is the difference of specifying reaction using UDF.

I was recomended to build the UDF based on multiple surface reaction, however people who performed this ignore CO2 and focused just on CO in the system. I couldn't understand this. I want to create a UDF file that cosiders the following reactions

C+O2=CO2

C+0.5O2=CO

C+CO2=2CO

another reaction would as well

2H+0.5O2=H2O

I am considering diffusion takes place that's I am not using the inputs of CFD while I am just focusing on UDF