Chemistry??

Question

3. Calculating Equilibrium Concentrations from Initial Concentrations

At 1280oC the equilibrium constant (Kc) for the reaction below is 1.1 x 10-3.

Br2 (g) --- > 2Br (g)

If the initial concentrations are [Br2] = 0.063 M and [Br] = 0.012 M, calculate the concentrations of these species at equilibrium. 

 

Answer 1

 

Step 1:

The chemical equation is .

Initial concentration of Br₂ is 0.063 M.

Initial concentration of Br is 0.012 M.

Equilibrium constant of the reaction is .

1 mole of Br₂ decomposes to 2 moles of Br.

Let be the change in concentration of Br₂ ,

then change in concentration of Br be .   (negative sign indicates decomposition)

Step 2:

Construct an ICE table.

Equilibrium Amount = Initial amount + Change in amount.

Find the equilibrium constant of the reaction.

The chemical equation is .

Equilibrium constant .

.

But equilibrium constant given as .

Step 3:

Now solve for x .

Find the equilibrium amount of Br₂ : .

Find the equilibrium amount of Br : .

So the equilibrium amount of Br is 0.00844 M.

The equilibrium amount of Br₂ is 0.06478 M.

Solution:

The equilibrium amount of Br is 0.00844 M.

The equilibrium amount of Br₂ is 0.06478 M.