Question

2NO (g) + Cl2 (g) <=> 2NOCl (g) (reversible)

equilibrium constat = 1 x 10^7 @ certain temp

NO = 2.8 x 10^-2 mol
Cl2 = 1.4 x 10^-3 mol
NOCl = 5.9 mol

all mixed in a 1.4 L flask

what is Qc and what direction will system go?

Answer 1

(NO) = 2.8E-2/1.4L = about 0.02M
(Cl2) = 1.4E-3/1.4L = about 0.001M
(NOCl) = 5.9/1.4L = about 4.21

Qc = (NOCl)^2/(NO)^2*(Cl2)
Qc = (4.21)^2/(0.02)^2*(0.001) = approx 5E7 but you should confirm that. Compare that with Kc =1E7
Qc > Kc; therefore, numerator is too large and/or denominator is too small which means rxn must shift to the left in order to decrease numerator4 and increase denominator.