South Pasadena • Chemistry
Name
Period
Date
7 · Kinetics and Equilibrium
STATION
1
•
EQUILIBRIUM EXPRESSIONS
Write the expression for the equilibrium constant for the reaction: Fe3+(aq) + SCN(aq)
[FeSCN2+]
Keq =
[Fe3+][SCN‒]
Write the expression for the equilibrium constant for the reaction: Fe3O4(s) + 4 H2(g)
[H2O]4
Keq =
[H2]4
Write the expression for the equilibrium constant for the reaction: Ca(OH)2(s)
Keq = [Ca2+][OH‒]2
FeSCN2+(aq)
3 Fe(s) + 4 H2O(g)
Ca2+(aq) + 2 OH-(aq)
7 · Kinetics and Equilibrium
STATION 2
Consider the equilibrium: 2NO(g) + O2(g)
•
EQUILIBRIUM CONSTANTS
2NO2(g).
At 100°C, the equilibrium concentrations for this system are:
[NO] = 0.50 M;
[O2] = 0.20 M;
[NO2] = 0.10 M
Write the expression for Keq and calculate its value at this temperature.
[NO2]2
(0.10)2
Keq =
=
= 0.2
2
[NO] [O2] (0.50)2(0.20)
Is this equilibrium system reactant or product-favored? Reactant-favored because Keq < 1.
Justify your answer.
7 · Kinetics and Equilibrium
STATION 3
•
LE CHÂTELIER’S PRINCIPLE
Consider the gaseous equilibrium: 2CCl4(g) + O2(g) + heat
2COCl2(g) + 2Cl2(g)
Predict the effect each change would have on the concentrations of each substance.
Add CCl4
[CCl4]

[O2]

Remove Cl2

Add COCl2
Shift
[COCl2]

[Cl2]








Increase temperature




Reduce container volume




Add a catalyst
‒
‒
‒
‒
Remove O2




‒
7 · Kinetics and Equilibrium
STATION 4
•
STRENGTHS
OF ACIDS
For each of the following acids, write the expression for the equilibrium constant.
Acid
Equation
Keq
Equilibrium Expression
[H+][OCl‒]
Keq =
[HOCl]
Hypochlorous acid, HOCl
HOCl(aq)
H+(aq) + OCl–(aq)
3.5 × 10–8
Nitrous acid, HNO2
HNO2(aq)
H+(aq) + NO2–(aq)
4.0 × 10–4
H+(aq) + C3H5O3–(aq)
1.4 × 10–4
H+(aq) + CN–(aq)
6.2 × 10–10
Lactic Acid, HC3H5O3
Hydrocyanic acid, HCN
HC3H5O3(aq)
HCN(aq)
List the acids from weakest to strongest: HCN < HOCl < HC3H5O3 < HNO2
Keq =
Keq =
[H+][NO2‒]
[HNO2]
[H+][C3H5O3‒]
[HC3H5O3]
Keq =
[H+][CN‒]
[HCN]
7 · Kinetics and Equilibrium
STATION
5
•
MORE LE
Consider the gaseous equilibrium: 2 SO2(g) + O2(g)
CHÂTELIER’S PRINCIPLE
2 SO3(g)
What changes can be made so the equilibrium system can be shifted to the right?
[ Add | Remove ] SO2(g)
[ Add | Remove ] O2(g)
[ Add | Remove ] SO3(g)
[ Increase | Decrease ] Volume
When the temperature is raised, the equilibrium system shifts to the left. Is this reaction endothermic or
exothermic? Justify your answer.
When temperature is raised, the reaction shifts away from heat. Heat must be a product, so the
reaction is exothermic.
7 · Kinetics and Equilibrium
STATION
6
• WHAT IS
EQUAL
Consider the equilibrium demonstration:
Chromate-Dichromate:
2H+(aq) + 2CrO42–(aq)
(yellow)
AT
EQUILIBRIUM?
Cr2O72–(aq) + H2O(ℓ)
(orange)
How can we tell when this system reaches equilibrium? _constant macroscopic (observable) property__
(color or concentration does not change.)
For every two yellow chromates that turn into one orange dichromate at equilibrium, what occurs?
One orange dichromate also turns into two yellow chromates.
Recall that pH is a measure of the [H+]. When this system reaches equilibrium, will the pH of the solution be
constant? _Yes___________ Justify your answer.
At equilibrium, [H+] does not change, so pH also will not change.
Consider the equilibrium: A(g)
B(g)
Draw a vertical line when equilibrium has been reached.
This reaction is _product__ -favored.
Estimate the Keq for this reaction: Keq ≈
[B] (0.75)
=
≈3
[A] (0.25)
7 · Kinetics and Equilibrium
STATION 7
+
Chromate-Dichromate Demo 2H (aq) +
2CrO42–(aq)
(yellow)
Cr2O72–(aq)
•
DEMOS
+ H2O(ℓ)
(orange)
When H+(aq) was added, the system shifted to the [ right | left ], changing from yellow to orange.
When OH–(aq) was added (removing H+), the system shifted to the [right | left], changing from orange to yellow.
NO2 Tubes Demo
2 NO2(g)
(amber)
N2O4(g) + heat
(colorless)
When the tubes were heated, the system shifted to the [ right | left ], changing from colorless to amber.
When the tubes were cooled, the system shifted to the [ right | left ], changing from amber to colorless.
CoCl42– Solutions Demo
Co2+(aq) + 4 Cl–(aq) + heat
(pink)
CoCl42–(aq)
(blue)
When HCl(aq) was added (adding Cl‒), the system shifted to the [ right | left ], changing from pink to blue.
When Ag+(aq) was added (removing Cl‒), the system shifted to the [ right | left ], changing from blue to pink.
When the tubes were heated, the system shifted to the [ right | left ], changing from pink to blue.
When the tubes were cooled, the system shifted to the [ right | left ], changing from blue to pink.
7 · Kinetics and Equilibrium
Potential Energy (kJ)
STATION
0
−10
−20
−30
−40
−50
−60
−70
−80
−90
−100
8
GRAPHS
Consider the reaction A  B
Draw the Potential Energy graph given the
following:
PE of A: −50 kJ
PE of B: −80 kJ
PE of Transition State: −30 kJ
T.S.
A
• POTENTIAL ENERGY
Ea
∆H
B
Label the Potential Energies of A, B, and Transition
State, Ea, and ∆H.
What are the values of:
Ea = (‒30 kJ) ‒ (‒50 kJ) = 20 kJ
Reaction Progress
∆H = (‒80 kJ) ‒ (‒50 kJ) = ‒30 kJ
Sketch the graph in a dashed line if a catalyst is added to the system so that the new Ea = 15 kJ.
7 · Kinetics and Equilibrium
STATION
9
•
State the ideas in Collision Theory.
A reaction happens when …
Molecules collide
With enough energy
In the correct orientation
KINETIC ENERGY GRAPHS
We can speed up a reaction by …
Increasing concentration, pressure, surface area
Increasing temperature
Adding a catalyst
Threshold
Energy
Kinetic Energy
Adding a Catalyst
 Color in completely the collisions that would result
in a reaction.
 Show what would change when a catalyst is added,
and shade in the new collisions that would result in
a reaction.
# of Collisions
# of Collisions
These are the Kinetic Energy graphs for a reaction.
Threshold
Energy
Kinetic Energy
Decreasing the Temperature
 Shade in completely the collisions that would result
in a reaction.
 Show what would change when the temperature is
lowered, and color in the collisions that would
result in a reaction at this lower temperature.