Question

Phosgene is a potent chemical warfare agent that is now outlawed by international agreement. It decomposes by the reaction: COCl₂ (g) ⇋   CO (g) + Cl₂ (g) K_c = 4.1 x 10^-5 (at 359°C)

Calculate the concentration of CO when 7.45 mol of phosgene decomposes and reaches equilibrium in a 10.0 liter flask. Multiply your answer by 10³ and enter that number to 2 decimal places.

Answer 1

Moles of CO = 7.45 mol

Volume of Flask = 10L

Molarity of COCl₂ = Moles/Volume = 7.45 mol / 10 L = 0.745 M

Given reaction is:

COCl₂ (g) ⇋   CO (g) + Cl₂ (g)

I(M) 0.745 0 0

C(M) -x +x +x

E(M) 0.745-x x x

Kc = [CO][Cl₂] /[COCl₂]

4.1 *10^-5 = x² / (0.745-x)

4.1 *10^-5 (0.745 -x) = x²

x² + (4.1 *10^-5)x - (3.05 *10^-5) = 0

x = 0.0055 = 5.5 *10^-3

Thus, at equilibrium , [CO] = x = 5.5 *10^-3 M

Now, if we multiply by 10³, then answer is 5.5