Thank you for the answer Ms. Swathi,

I had already gone through the documentation but it did not help much. Here we have the mass balance and the energy balance equations respectively:

I have a S_i which is not 0. In the energy balance the second term is 0 because I do not have convection (there is no inlet/outlet or current at all), the thirdt term is 0 because I do not haven conduction diffusion or dissipation, and the fourth term is 0 because I have not defined any sources of heat. Why is the temperature decreasing?

I have thought that maybe this comes from the equation of state (ideal gases): pV=nRT. The generation of a species would increase the n/V (moles/m3). I guess that then Ansys considers constant pressure, which requires that the temperature decreases. Is that the case?

Thank you once again for the support.