Clarification regarding how duplicate reactions are handled

[H V]

Hello, 

I was wondering how duplciate reactions are handled / what the differences are in three different cases

1. if the file has both A + B <-> C + D and C + D <-> A + B, how is the effective rate computed? The documentation says the rates are summed, but does it take into account that the duplicate equation gives the backward rate while the firs one has the rate expression for the forward rate. 

2. What is the difference between having these two reactions declared as duplicates or not? A + B -> C + D and C + D -> A + B. 

Thanks!

[Ray Speth]

Hi,

In the first case, if the two reactions are marked as duplicates, then both rates are calculated independently, and contribute to the summations needed to calculate the rates of production / destruction of the species A, B, C, and D. The fact that both a forward rate and a reverse rate contribute to production of C and D, for example, is why the reactions must be declared as duplicates -- the assumption otherwise is that it is user error to include the reaction written in both directions.

In the second case, the reactions should not be declared duplicate -- there is only one rate for production of each species involved. This is the approach available for explicitly specifying reverse rate constants. Arguably, declaring these as duplicates should be considered an error, but Cantera does not currently do so as long as both reactions are marked as such. There is no difference in the calculation of the rates either way.

Regards,

Ray