1. Kc Equilibrium Constant…
We have discussed the shifting of equilibrium position in a qualitative way, but the degree of shift can be quantified Kc

2. [reactant] : [product]
Equilibrium Constant…
The value of Kc tells us how the equilibrium position is shifted:
Kc = 1
[reactant] : [product]
1 : 1

3. [reactant] < [product]
Equilibrium Constant…
The value of Kc tells us how the equilibrium position is shifted:
Kc > 1
[reactant] < [product]
Equilibrium is to the right

4. [reactant] > [product]
Equilibrium Constant…
The value of Kc tells us how the equilibrium position is shifted:
Kc < 1
[reactant] > [product]
Equilibrium is to the left

5. Equilibrium Constant…
aA + bB cC + dD
Kc = [C]c[D]d
[A]a[B]b

6. Equilibrium Constant… 2SO2 + O2 2SO3 Kc = [SO3]2 [SO2]2[O2] = 0.72
0.4 moldm moldm moldm-3
Kc = [SO3]2
[SO2]2[O2] =
0.42*0.2
= 15.3
What does this tell us about the eqm position?

7. Equilibrium Constant… 2SO2 + O2 2SO3 Kc = 15.3
0.4 moldm moldm moldm-3
Kc = 15.3
Kc is greater than one so the equilibrium is shifted toward the right.

8. Equilibrium Constant… 2SO2 + O2 2SO3
0.4 moldm moldm moldm-3
Now we need to look at the units for the equilibrium constant.
Kc = (moldm-3)2
(moldm-3)2 (moldm-3)
= 1
(moldm-3) = mol-1dm3

9. Equilibrium Constant…
2SO2 + O2 2SO3
Therefore Kc = 15.3 mol-1dm3

10. Equilibrium Constant…
What ways can we change the value of Kc?

11. Equilibrium Constant…
The only factor affecting Kc is:
Temperature
Concentration and pressure do not affect Kc.
As catalysts do not change the equilibrium position they will not affect Kc either.