Ex.15. Why the inert species (C5H7O2N) is disregarded in -formula

[MichaelZ20]

"Nta is assumed to degrade in the presence of biomass and oxygen by the reaction:
HNta2- + 1.62O2 + 1.272H2O + 2.424H+ = 0.576C5H7O2N + 3.12H2CO3 + 0.424NH4+
...The Nta reaction converts 1 mol HNta2- (C6H7O6N) to 0.576 mol C5H7O2N, where the latter is chemically inert so that its concentration can be discarded."

Why the inert species (C5H7O2N) is disregarded in mass balance in -formula. After all, C, H, O and N elements of the reactants are used for its formation.

[dlparkhurst]

The equations that are solved for solution equilibrium include a mole balance equation, say for carbon, and mass-action expressions for every aqueous carbon species. The mole balance equation includes all the carbon species that the total carbon in solution can be distributed among based on the mass-action equations. Because C5H7O2N is assumed not to react with other carbon species, it should not be included in the carbon mole balance equation.

You could include a reactive C5H7O2N by defining a mass-action equation for it, but in all probability,if you use a realistic log K, C5H7O2N thermodynamically would  decompose immediately to other C, H, O, an N species.

If you assume C5H7O2N is inert and want to keep track of the amount that is created, you could include a new "element". In the attached file, an element "[C5H7O2N]" is added and the -formula is modified to include the new element and the graph is modified to plot the concentration of [C5H7O2N].

Code: [Select]

-formula C -3.12 H -1.968 O -4.848 N -0.424 [C5H7O2N] -0.576 Nta 1