Equilibrium & Kinetics
Dr. Ron Rusay
Summer 2004
© Copyright 2004 R.J. Rusay
Dynamic Equilibrium
“The Pennies”
• Organize into groups of 3-4.
• Dr. R will assign your group a number.
• In your group, select one person as:
1) Money Keeper
2) Recorder
3) Transfer Agent (Calculating agent)
4) Auditor (Can be combined with #3)
• Send the Recorder to see Dr. R. for your accounting form.
Be sure to record other group member names on the form.
• After recording all of the names send the Money Keeper
to see Dr. R. for your capital stake.
• Await instructions for phase I.
Dynamic Equilibrium
“The Pennies”
Phase I:
Phase II:
There will be 8 phases. You can begin and go through them at your own pace.
Let Dr. R know when you have completed four phases. Stop at this point. Give
Dr. R. the accounting form when completed.
Pennies Results
Group
Rate
ini tial
ch ange
fin al
ini tial
ch ange
fin al
IA
-50%
40
-10%
0
IIA
-25%
20
IIB
-50%
20
IIIA
-10%
20
IIIB
-50%
20
IVA
-50%
0
IVB
-25%
40
20
-50%
20
-10%
25
-25%
15
-50%
28
-10%
12
-50%
10
-50%
30
-25%
12
-50%
28
-10%
20
-25%
13
-50%
31
-10%
9
-50%
12
-50%
28
-25%
9
31
-10%
27
-25%
14
-50%
33
-10%
7
-50%
13
-50%
27
-25%
33
27
14
34
6
13
27
ini tial
ch ange
fin al
-50%
ini tial
ch ange
fin al
ini tial
ch ange
fin al
ini tial
ch ange
fin al
ini tial
ch ange
fin al
ini tial
ch ange
fin al
IB
7
-25%
-50%
-50%
-10%
-50%
-25%
-10%
-50%
22
-25%
18
-50%
14
-50%
26
-10%
19
-50%
21
-25%
25
-10%
15
-50%
25
-25%
15
-50%
10
-50%
30
-10%
14
-50%
26
-25%
30
-10%
10
-50%
27
-25%
13
-50%
8
-50%
32
-10%
14
-50%
26
-25%
32
-10%
-50%
27
13
33
14
26
33
7
7
7
Dynamic Equilibrium
“The Pennies”
Simulator:
http://mc2.CChem.Berkeley.EDU/Java/equilibrium/
Class Results
http://ep.llnl.gov/msds/chem120/equil-graph.html
Dynamic Equilibrium
“The Pennies”
http://ep.llnl.gov/msds/chem120/equil-graph.html
Chemical Equilibrium
QuickTime™ and a
Intel Indeo® Video R3.2 decompressor
are needed to see this picture.
Reaction Diagram of O3 decomposing
O2 (g) + O(g)
O3 (g)
[formation]
O3 (g) + O(g)
2 O2 (g)
[breakdown (decomposing)]
Chemical Equilibrium
 Most of the reactions considered until now
have had reactants react completely to form
products. These reactions “went” only in one
direction. []
 Some reactions can react in either direction.
They are “reversible”. [
]When this occurs
some amount of reactant(s) will always
remain at the end of change. Weak acids and
bases follow this type.
Chemical Equilibrium
(Definitions)
A chemical system where the
concentrations of reactants and
products remain constant over time.
 On the molecular level, the system is
dynamic: The rate of change is the
same in both the forward and reverse
directions.

Equilibrium Expression **

For any equilibrium
Reactants
Products

The Equilibrium Expression relates the
concentrations of products and reactants.

The value of the Equilibrium constant, K, indicates
which position of equilibrium is favored.
K=
Products
___________
Reactants
Position of Equilibrium
K=
Products
___________
Reactants
If K is large then there will be a larger
concentration of products at equilibrium than
of reactants. The position of equilibrium
favors products.
 If K is small then there will be a larger
concentration of reactants at equilibrium than
of products. The position of equilibrium favors
reactants.

Law of Mass Action **
(The Equilibrium Expression)
 For
a reaction:
• jA+kB
lC+mD
 The law of mass action is represented
by the Equilibrium Expression: where K
is the Equilibrium Constant. (Units for K
will vary.)
l
C D
K
j
A B
m
k
The Equilibrium Expression **
Concentration or partial pressure is used.
 Concentration of gases depends on the partial
pressure of the gas:

 (Higher

pressure = Higher concentration)
Concentration of solutions depends on the
solute to solution ratio (molarity, M).
l
C D
K
j
A B
m
k
Equilibrium Expression **
_ O2(g)  _ NO2(g) + _ H2O(g)

_ NH3(g) +

The following Equilibrium Expression can have the
amounts uniformly expressed as units of
concentration mol/L (M), or as units of pressure
(atm).
Equilibrium Expression **


4 NH3(g) + 7 O2(g)  4 NO2(g) + 6 H2O(g)
The following Equilibrium Expression can have the
amounts uniformly expressed as units of
concentration mol/L (M), or as units of pressure
(atm).
4
6
NO2 H 2O
K
4
7
NH3 O2
Equilibrium Expressions
If
a reaction is re-written where the
reactants become products and
products-reactants, the new Equilibrium
Expression is the reciprocal of the old.
Knew = 1/Koriginal
When the entire equation for a reaction
is multiplied by a molar factor n,
Knew = (Koriginal)n
Heterogeneous Equilibria
Equilibria that involve more than one
phase.

• CaCO3(s)  CaO(s) + CO2(g)
K = [CO2 ]
Heterogeneous Equilibria

• CaCO3(s)  CaO(s) + CO2(g)
K = [CO2 ]
 The position of a heterogeneous
equilibrium does not depend on the
amounts of pure solids or liquids
present.
Le Châtelier’s Principle**
.
. . If change is imposed on a system
at equilibrium, the system will shift in a
direction that tends to reduce that
change and re-establish the original
equilibrium’s relationship of reactants
products.
Le Châtelier’s Principle **
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Changes on the System **

1. Concentration: The system will shift
concentrations away from the added
component. K remains the same.

2. Temperature: K will change depending
upon the reaction. If endothermic, heat is a
reactant, exothermic, heat is a product.
Increasing T will increase or decrease K.
Endo  K increases; Exo  K decreases.
Temperature Effects on
the NO2  N2O4 Equilibrium
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Changes on the System **
(continued)

3. Pressure:
A) Changing the partial pressure of one
gas is like changing its concentration
• It has the same effect as changing the
concentration on the position of equilibrium

B) Increasing the pressure of the entire
system causes the position of equilibrium
to shift toward the side of the reaction with
the fewer gas molecules.
Kp = Kc (RT)n
n = nproducts - nreactants
Changes on the System **
(continued)

3. Pressure:
C). Addition of inert gas does not affect the
equilibrium position.
D). Decreasing the volume of the system
increases its pressure shifting the equilibrium
toward the side with fewer moles.
• Reduces the pressure by reducing the total
number of gas molecules
• [Le Châtelier’s Principle: if pressure is increased
the system shifts to minimize the increase.]
Changes on the System **
(continued)
4. The Effect of Catalysts
 A catalyst lowers the activation energy barrier
for any reaction….in both forward and reverse
directions!
 A catalyst will decrease the time it takes to
reach equilibrium.
 A catalyst does not effect the composition of
the equilibrium mixture.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Reaction Diagram of O3 decomposing
Catalysts Lower the Energy of Activation
with Freon
O3
O2
Catalytic Destruction of Ozone
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
QuickTime™ and a
Sorenson Video decompressor
are needed to see this picture.
Satellite Images of the Ozone
Hole
Homeostasis
Physiological Equilibrium
http://physioweb.med.uvm.edu/homeostasis/
“Pools, Balance, Equilibrium, Bio-feedback”
 Let Pool be a person’s body weight.
 Let Input and Output be energy.
 (What are possible sources of energy input
and forms of energy output?)
 Consider a 70 kg individual with Input =
Output = 2000 Cal / day, how do you
compare?
