@ReactionUra Based on these chemical reactions, I'm guessing x is NOT a constant, but rather a variable. However, since I'm not a traditionally trained chemist, this answer includes x = 0.
Since what you want are numerical values, i.e., floating point values, for the unknowns, I suggested fsolve.
(To save space, I have made a sequence (seq) of equations which Maple reads as as eq||n where n is an integer that counts from 1 to 12 by increments of 1. 12 equations, 12 unknowns.)
That said, many of the values are negative. Does this make physical sense to you? (Because it does not to me.) I'm wondering if there may be sign problems in the equations.