1. Equilibrium Constants

2. Recall: At equilibrium, the rate of the forward and reverse reactions are equal

3. The Equilibrium Constant, Keq
For the reaction:
aA + bB  cC + dD
At equilibrium:
rfwd = rrev
kfwd[A]a[B]b = krev[C]c[D]d
kfwd = [C]c[D]d
krev [A]a[B]b
Keq = [C]c[D]d
[A]a[B]b
Sub in rate law equation
Rearrange
Sub in Keq for
kfwd/krev
Equilibrium constant

4. Examples
Write the equilibrium constant expression for the following two reactions

5. Heterogeneous Equilibria
Equilibrium systems can involve all states of matter
However, the concentration of a pure solid or liquid cannot change
Therefore, equilibrium constant expressions will not include solids and liquids

6. Keq = [C]c[D]d
[A]a[B]b
Magnitude of Keq
Keq >> 1 At equilibrium there is more products than reactants. The reaction is product favoured
Keq = 1 At equilibrium there is an equal amount of products and reactants
Keq << 1 At equilibrium there is more reactants than products. The reaction is reactant favoured

7. Example Calculate the value of Keq for the following system
At Equilibrium:
[CO2] = mol/L
[H2] = mol/L
[CO] = [H2O] = mol/L

8. Practice
P #1-6
P. 448 #1-9