Problems about the standard state enthalpy
 

Hi, everyone! I'm modeling the heterogeneous reactions with ansys fluent, and now I have some problems in defining the standard state enthalpy (SSE). I have two reactions:
R1: aA→bB
R2: mB→nC
Now I set the SSE of A equals to 0, and SSE of B equals to 255kJ/kg, therefore the reaction heat of R1 is 255kJ/kg. Now I have known the reaction heat of R2 is -42kJ/kg, how should I set the SSE of C?

More generally, for the reaction:
aA+bB→cC+dD
If SSE of all reactants (hA, hB, hC, hD) is given, how to calculate the reaction heat of this reaction?

Thanks a lot for your kind help.