AT A CERTAIN TEMPERATURE, THE REACTION

CO(g) + 2H2(g) <----> CH3OH (g)
has Kc = 0.500
CO= 0.180 M
H2= 0.220 M
WHAT IS THE CONCENTRATION OF CH3OH?

3 answers

It helps to read if you don't put everything in caps.
..........CO + 2H2 ==> CH3OH
initial..0.180.0.220.....0
change.....-x....-2x......x
equil...0.180-x..0.220-2x..x

Substitute into Kc expression and solve for x.
i don't know if your are right but the answer that they give is 4.36x10'-3
0.00436 is close but not quite correct. To prove that substitute back into the Kc expression and see if you get 0.5. You don't. I think you obtain 0.55.
I solved the cubic equation and obtained 0.003959 (which of course is too many significant figures) but if you substitute that into Kc you get exactly 0.500. I would round the answer to 0.00396M and that produces a Kc of 0.500 also.