Write me a specific problem. This is too vague to discuss in generalities.
The reaction 2 N2
(g) + O2
(g) is initiated in a reactor which also contains some unreactive He gas (the initial concentration/partial pressure of this gas is known, and by definition of being unreactive we know that the number of moles of He do not change). Can we calculate the concentrations or partial pressures of the 4 constituents of the system (N2
and He) at any time t? If yes, what ODEs do we need to write to do so? (We will need one more ODE than the 3 based on the 3 reacting species, an ODE for He)
At best I would like to consider the isothermal case directly, but otherwise I'd be happy to look at the constant volume, constant temperature case and see if we can come up with any ideas from there.
As in, if there are gases not involved in reactions which are still present in the same container, we cannot account for them or calculate anything for the system (as they would affect partial pressure/concentration calculations). Unless we can write an ODE for them too? Or there may be some other way?