How many moles??

Question

At a certain temperature, Kc equals 1.4 x 10^2 for the reaction: 2CO(g)+O2(g) --> 2CO2 (g). If a 2.50-L flask contains 0.400 mol of CO2 and 0.100 mol of O2 at equilibrium, how many moles of CO are also present in the flask?

Answer 1

2CO(g) + O2(g) --> 2CO2 (g)

Kc = [CO2]² / [CO]²[O2]

1.4x10² = (0.400)² / (x)²(0.100)

x = mols CO = 0.0338 moles

(be sure to check the math)