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) Kc = 7.5 x 10-5 (at 362°C) Calculate the concentration of CO when 7.73 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. HINT: Look at sample problem 17.9 in the 8th ed of Silberberg. Write a Kc expression. Calculate the initial concentration of phosgene. Do an ICE chart. Find the concentration of CO.

Answer 1

Answer:

[CO] = 7.61x10⁻³M

7.61x10⁻³x10³ = 7.61

Explanation:

For a generic equation aA + bB ⇄ cC + dD, the constant of equilibrium (Kc) is:

$Kc = \frac{[C]^cx[D]^d}{[A]^ax[B]^b}$

We need to know the molar concentrations in the equilibrium. In the beginning, there is only COCl₂, and its concentration is the number of moles divided by the volume:

[COCl₂] = 7.73/10.0 = 0.773 M

So, the equilibrium will be:

COCl₂(g) ⇆ CO(g) + Cl₂(g)

0.773             0           0      Initial

-x                    +x         +x     Reacts

0.773-x            x           x       Equilibrium

Supposing that x<<0.773, then:

$Kc = \frac{x*x}{0.773}$

7.5x10⁻⁵ = x²/0.773

x² = 5.7975x10⁻⁵

x = √5.7975x10⁻⁵

x = 7.61x10⁻³ M

The supposing is correct, so [CO] = 7.61x10⁻³ x 10³ = 7.61