1. Equilibrium: LeChatelier’s
Principle, Ksp, and Keq
Until this point most of our reactions
have gone to completion forming
water, gas, or a precipitate. In
equilibrium reactions, however, there
is product and reactant at the same
time.
NO2

2. Equilibrium Constant
2 SO2
+
O2
<->
2 SO3
(air pollution)
N2
+
O2
<->
2 NO2
(air pollution)
Keq
=
Equilibrium Constant
=
[Concentration of Products]
[Concentration of Reactants]
Keq
=
[SO3]2
[SO2]2 [O2]

3. Calculate the Keq for
the following reaction:
CH4
+
2 H2S
<->
CS2
+
4 H2
(0.45M)
(0.30M
(0.35M)
(0.20M)
(0.35) (0.0016)
Keq
=
[CS2] [H2]4
=
0.013
[CH4] [H2S]2
(0.45) (0.09)
=1
Equilibrium favors prod. & react.
>1
Equilibrium favors products
<1
Equilibrium favors reactants

4. Le Chatelier’s Principle:
If you disturb a reaction at
equilibrium, the reaction returns
to equilibrium in such a direction
to partially undo the disturbance.

5. A Couple of Equilibrium Questions...
2 CO (g)
+
O2 (g)
<->
2CO2 (g)
E= -563 kjoules
Stress
Shift
Why
Add heat
Add O2
Add catalyst
Decrease Pressure
Pb(NO3)2 (s) <->
Pb+2 (aq)
+
2NO3-1 (aq)
E= +34 kjoules
Stress
Shift
Why
Add NaCl
Add NH4C2H3O2
Increase temperature
Increase pressure

6. Ksp: Solubility Product
Constant
Ksp has major importance in slightly
soluble compounds such as uric acid and
the cause of gout in humans, and in a
natural contaminant of drinking water
FeS.

7. Calculation of Ksp...
Ksp
=
BaSO4
(s)
<->
Ba+2 (aq)
+ SO4-2 (aq)
Ksp
=
[Ba+2] [SO4-2]
Ksp for BaSO4
1.1x 10-10 M
=
Ba+2 ion
= Sq. Rt. 1.1 x 10-10
=
1.05 x 10-5
SO4-2 ion
=
same as above