For the reaction so2 (g) + no2 (g) so3 (g) + no (g), the equilibrium constant kc is 18.0 at 1200ºc. if 1.0 mole of so2and 2.0 moles of no2 are placed in a 20.0-l container, what concentration of so3 will be present at equilibrium?

a. 0.048 mol/l

b. 0.11 mol/l

c. 0.95 mol/l

d. 2.22 mol/l

e. 18 mol/l

when:

[SO2] = 1mol/20L = 0.05 M

[NO2] = 2mol / 20L = 0.1 M

by using ICE table:

SO2 (g) + NO2 (g) ↔ SO3 (g) + NO (g)

initial 0.05 0.1 0 0

change - X - X + X + X

Equ (0.05-X) (0.1-X) + X + X

when Kc = [SO3][NO]/[SO2][NO2]

by substitution:

18 = X^2 / (0.05-X) (0.1-X) by solving this equation for X

∴X (1,2) = - 1/34√1.17+27/340, 1/34√1.17+27/340

we can neglect the negative one

∴X = 0.11 mol/L