Question

A sealed 1.0-L flask, initially containing 0.20 M COCl2, 0.20 M Cl2, and 0.20 M CO, is heated to 700 K

and allowed to come to equilibrium.

COCl2(g) ⇌ Cl2(g) + CO(g) Kc = 0.12 at 700 K

a. What are the molar concentrations of COCl2, Cl2, and CO once the reaction has reached equilibrium

at 700 K?

COCl2:_______________________________

Cl2:_______________________________

CO:_______________________________

b. 0.10 mol COCl2 is added to the equilibrium mixture. What are the molar concentrations of COCl2,

Cl2, and CO once equilibrium is re-established?

COCl2:_______________________________

Cl2:_______________________________

CO:_______________________________

Answer 1

   COCl2(g) ⇌ Cl2(g) + CO(g)

I          0.2               0.2       0.2

C        -x                   +x         +x

E      0.2-x             0.2+x      0.2+x

       Kc   = [Cl2][CO]/[COCl2]

     0.12   = (0.2+x)(0.2+x)/(0.2-x)

     0.12*(0.2-x)   = (0.2+x)(0.2+x)

       x = -0.033

[COCl2] = 0.2-(-0.033) = 0.233M

[CO]      = 0.2+x = 0.2-0.033   = 0.167M

[Cl2]   = 0.2+x     = 0.2-0.033   = 0.167M

               COCl2(g) ⇌ Cl2(g) + CO(g)

   I          0.1                0             0

C           -x                +x             +x

E      0.1-x                +x             +x

           Kc   = [CO][Cl2]/[COCl2]

          0.12   = x*x/0.1-x

            x²   = 0.12*(0.1-x)

               x = 0.065

           [COCl2]   = 0.1-x = 0.1-0.065 = 0.035M

          [CO]        = x = 0.065M

          [Cl2]      = x = 0.065M