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Kinetics
Lesson 5
PE Diagrams
Mechanisms
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Potential Energy
Activated Complex
Products
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Potential Energy
Activated Complex
Products
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
max
Potential Energy
low
high
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
max
Potential Energy
low
Kinetic Energy
high
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
max
Potential Energy
high
low
Kinetic Energy
high
min
low
Potential and Kinetic Energy Changes during a Collision
Endothermic
Reactants
Activated Complex
Products
max
Potential Energy
high
low
Uphill- endothermic!
Kinetic Energy
high
min
low
Pick the slow and fast reaction
Pick the slow and fast reaction
Ea
Ea
Pick the slow and fast reaction
Ea
Ea
Slow
Fast- low Ea
Reaction Mechanisms
Consider the following reaction:
4 HBr(g)
+
O2(g) →
2H2O(g)
+
2Br2(g)
Watch Simulation- set both temperature and mass to the
highest setting. Set red to 1 and blue to four and remove the
barrier. How often do all five particles collide?
There are five reactant particles.
If there are three or more reactant particles they will not
likely react in one step.
They will react in a series of steps, which is a mechanism.
Mechanism 1 .
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
+2HBr(g)
→
HOOBr(g)
slow
2HOBr(g)
→
fast
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 Cancel out identical formulas to get the overall equation.
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
+2HBr(g)
→
HOOBr(g)
slow
2HOBr(g)
→
fast
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 Cancel out identical formulas to get the overall equation.
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
+2HBr(g)
→
HOOBr(g)
slow
2HOBr(g)
→
fast
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 Cancel out identical formulas to get the overall equation.
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
+2HBr(g)
→
HOOBr(g)
slow
2HOBr(g)
→
fast
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 Intermediates are produced and then consumed and
cross out from right (first) and left (second).
HBr(g) +
O2(g)
→
HOOBr(g)
slow
HBr(g) + HOOBr(g) →
2HOBr(g)
+2HBr(g)
2HOBr(g)
→
fast
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 What is left is the overall reaction.
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
+2HBr(g)
→
HOOBr(g)
slow
2HOBr(g)
→
fast
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 What is left is the overall reaction.
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
4HBr(g)
+
→
HOOBr(g)
slow
2HOBr(g)
fast
+2HBr(g)
→
2H2O(g)+
2Br2(g)
O2(g)
→
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1 Step 1, which is the slow step, is called the rate
determining step and has the highest activation energy.
HBr(g) +
O2(g)
→
HOOBr(g)
slow
HBr(g) + HOOBr(g) →
2HOBr(g)
4HBr(g)
+
2HOBr(g)
fast
+2HBr(g)
→
2H2O(g)+
2Br2(g)
O2(g)
→
2H2O(g)+
2Br2(g)
PE
Reaction Path
fast
Mechanism 1
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
4HBr(g)
+
→
HOOBr(g)
slow
2HOBr(g)
fast
+2HBr(g)
→
2H2O(g)+
2Br2(g)
O2(g)
→
2H2O(g)+
2Br2(g)
A potential energy diagram for this
reaction might look like this.
PE
Reaction Path
fast
Mechanism 1
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
4HBr(g)
+
→
HOOBr(g)
slow
2HOBr(g)
fast
+2HBr(g)
→
2H2O(g)+
2Br2(g)
O2(g)
→
2H2O(g)+
2Br2(g)
A potential energy diagram for this
reaction might look like this.
PE
Reaction Path
fast
Mechanism 1
HBr(g) +
O2(g)
HBr(g) + HOOBr(g) →
2HOBr(g)
4HBr(g)
+
→
HOOBr(g)
slow
2HOBr(g)
fast
+2HBr(g)
→
2H2O(g)+
2Br2(g)
O2(g)
→
2H2O(g)+
2Br2(g)
highest
A potential energy diagram for this
Mechanism has three humps
PE
The slow step has the highest Ea
fast
Ea(rev)
Ea
Reaction Path
The Rate Determining Step
The slowest step in the reaction mechanism is called the ratedetermining step. It has the highest Ea. To increase the rate,
you must increase the rate of this step. Increasing the rate of a
fast step will not increase the rate of the overall reaction.
Identifying a Catalyst in a Mechanism
A catalyst is not consumed in the reaction. It is used in one
step; it speeds up the reaction, and then is regenerated in a
later step. A catalyst will cancel out but will be on the left
side in an earlier step than on the right side.
Identifying a Catalyst in a Mechanism
A catalyst is not consumed in the reaction. It is used in one
step; it speeds up the reaction, and then is regenerated in a
later step. A catalyst will cancel out but will be on the left
side in an earlier step than on the right side.
C
→
→
C
Identifying a Catalyst in a Mechanism
A catalyst is not consumed in the reaction. It is used in one
step; it speeds up the reaction, and then is regenerated in a
later step. A catalyst will cancel out but will be on the left
side in an earlier step than on the right side.
C
→
→
C
Identifying a Catalyst in a Mechanism
A catalyst is not consumed in the reaction. It is used in one
step; it speeds up the reaction, and then is regenerated in a
later step. A catalyst will cancel out but will be on the left
side in an earlier step than on the right side.
C
→
→
C
An intermediate is produced and then consumed. It will be
on the right side in an earlier step than on the left side.
Identifying a Catalyst in a Mechanism
A catalyst is not consumed in the reaction. It is used in one
step; it speeds up the reaction, and then is regenerated in a
later step. A catalyst will cancel out but will be on the left
side in an earlier step than on the right side.
C
→
→
C
An intermediate is produced and then consumed. It will be
on the right side in an earlier step than on the left side.
I
→
→
I
Identifying a Catalyst in a Mechanism
A catalyst is not consumed in the reaction. It is used in one
step; it speeds up the reaction, and then is regenerated in a
later step. A catalyst will cancel out but will be on the left
side in an earlier step than on the right side.
C
→
→
C
An intermediate is produced and then consumed. It will be
on the right side in an earlier step than on the left side.
I
→
→
I
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
Overall Equation:
Catalyst:
Intermediate:
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
Overall Equation:
Catalyst:
Intermediate:
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
Overall Equation:
Catalyst:
Intermediate:
C
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
Overall Equation:
Catalyst:
Intermediate:
C
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
C
CD
Overall Equation:
Catalyst:
Intermediate:
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
C
CD
Overall Equation:
Catalyst:
Intermediate:
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
Overall Equation:
Catalyst:
D
Intermediate:
C
CD
+
D
Mechanism 2
1.
A
+
B
→
C
2.
C
+
D
→
CD
3.
CD
+
E
→
ABE
Overall Equation:
A +
B + E → ABE
Catalyst:
D
Intermediate:
C
CD
+
D
Mechanism 3
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
PE
Reaction Path
Overall Reaction:
Intermediates:
Mechanism 3
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
PE
Reaction Path
Overall Reaction:
Intermediates:
Mechanism 3
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
PE
Reaction Path
Overall Reaction:
Intermediates:
Br2 + OCl2 → BrOCl + BrCl
Mechanism 3
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
PE
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
Cl
Mechanism 3
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
PE
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
Mechanism 3
PE
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
200 kJ
Mechanism 3
PE
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
200 kJ
Mechanism 3
PE
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
200 kJ
600 kJ
Mechanism 3
PE
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
200 kJ
600 kJ
400 kJ
Mechanism 3
PE
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
200 kJ
600 kJ
400 kJ
300 kJ
Mechanism 3
PE
Step 1
Step 2
Step 3
Br2
Br + OCl2
Br + Cl
→ 2Br
→ BrOCl + Cl
→ BrCl
800
600
400
200
Reaction Path
Overall Reaction:
Br2 + OCl2 → BrOCl + BrCl
Intermediates:
Br
ΔH
=
Ea (forward) =
Ea (reverse) =
The enthalpy of Br
The enthalpy of BrCl
Cl
200 kJ
600 kJ
400 kJ
300 kJ
400 kJ
Mechanism 4
The following mechanism shows how chlorine-containing
fluorocarbons destroy the ozone layer. Ozone is O3 and O
1.
CFCl3
2.
Cl
3.
ClO
→
CFCl2 +
+
O3
→
ClO
+
O2
+
O
→
Cl
+
O2
Overall Reaction:
Intermediates:
Cl
Mechanism 4
The following mechanism shows how chlorine-containing
fluorocarbons destroy the ozone layer. Ozone is O3 and O
1.
CFCl3
2.
Cl
3.
ClO
→
CFCl2 +
+
O3
→
ClO
+
O2
+
O
→
Cl
+
O2
Overall Reaction:
Intermediates:
Cl
Mechanism 4
The following mechanism shows how chlorine-containing
fluorocarbons destroy the ozone layer. Ozone is O3 and O
1.
CFCl3
2.
Cl
3.
ClO
→
CFCl2 +
+
O3
→
ClO
+
O2
+
O
→
Cl
+
O2
Overall Reaction:
Intermediates:
Cl
CFCl3 + O3 + O → CFCl2
+ 2O2 + Cl
Mechanism 4
The following mechanism shows how chlorine-containing
fluorocarbons destroy the ozone layer. Ozone is O3 and O
1.
CFCl3
2.
Cl
3.
ClO
→
CFCl2 +
+
O3
→
ClO
+
O2
+
O
→
Cl
+
O2
Cl
Overall Reaction:
CFCl3 + O3 + O → CFCl2
Intermediates:
Cl
ClO
+ 2O2+ Cl
Determine the Missing Step of the Mechanism
Mechanism 5
Overall:
A
+
B
→
C
C
+
D
→
B
+
AD
A
+
D
+
E
→
ADE
Determine the Missing Step of the Mechanism
Mechanism 5
Overall:
A
+
B
→
C
C
+
D
→
B
+
AD
A
+
D
+
E
→
ADE
Determine the Missing Step of the Mechanism
Mechanism 5
Overall:
A
+
B
→
C
C
+
D
→
B
+
AD
A
+
D
+
E
→
ADE
Put in step 3 so that you get the overall reaction
Determine the Missing Step of the Mechanism
Mechanism 5
A
+
B
→
C
C
+
D
→
B
+
AD
+
D
+
E
→
ADE
AD
Overall:
A
Put in AD to cancel
Determine the Missing Step of the Mechanism
Mechanism 5
Overall:
A
+
B
→
C
C
+
D
→
B
+
AD
AD
+
A
+
E
→
ADE
Put in AD to cancel
→
D
+
Determine the Missing Step of the Mechanism
Mechanism 5
Overall:
Put in E
A
+
B
→
C
C
+
D
→
B
+
AD
AD
+
E
→
A
+
D
+
E
→
ADE
Determine the Missing Step of the Mechanism
Mechanism 5
Overall:
Put in ADE
A
+
B
→
C
C
+
D
→
B
AD
+
E
→
ADE
A
+
D
+
E
+
AD
→
ADE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
C
+
D
→
CD
CD
+
E
→
ABE
+
D
A
+
B
+
E
→
ABE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
C
+
D
→
CD
CD
+
E
→
ABE
+
D
A
+
B
+
E
→
ABE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
C
+
D
→
CD
CD
+
E
→
ABE
+
D
A
+
B
+
E
→
ABE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
C
+
D
→
CD
CD
+
E
→
ABE
+
D
A
+
B
+
E
→
ABE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
→
C
C
+
D
→
CD
CD
+
E
→
ABE
+
D
A
+
B
+
E
→
ABE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
→
C
C
+
D
→
CD
CD
+
E
→
ABE
+
D
A
+
B
+
E
→
ABE
Determine the Missing Step of the Mechanism
Mechanism 6
Overall:
A
+
B
→
C
C
+
D
→
CD
CD
+
E
→
ABE +
A
+
B
+
E
→
D
ABE
Determine the Missing Step of the Mechanism
Mechanism 7
Overall:
CFCl3 →
CFCl2 +
ClO
O
+
→
O + CFCl3 + O3 →
Cl
Cl
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
Overall:
CFCl3 →
CFCl2 +
ClO
O
+
→
O + CFCl3 + O3 →
Cl
Cl
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
CFCl2 +
Cl
Cl
ClO
Overall:
+
O
→
O + CFCl3 + O3 →
Cl
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
CFCl2 +
Cl
Cl
ClO
Overall:
+
O
→
O + CFCl3 + O3 →
Cl
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
Cl
ClO
Overall:
+
+
CFCl2 +
Cl
O3
O
→
O + CFCl3 + O3 →
Cl
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
Overall:
CFCl2 +
Cl
+
O3 →
ClO
+
O
Cl
ClO
+
→
Cl
O + CFCl3 + O3 →
O2
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
Overall:
CFCl2 +
Cl
+
O3 →
ClO
+
O
Cl
ClO
+
→
Cl
O + CFCl3 + O3 →
O2
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
Overall:
CFCl2 +
Cl
+
O3 →
ClO
+
O
Cl
ClO
+
→
Cl
O + CFCl3 + O3 →
O2
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
Overall:
CFCl2 +
Cl
+
O3 →
ClO
+
O
Cl
ClO
+
→
Cl
O + CFCl3 + O3 →
O2
+
O2
CFCl2 + 2O2
+
Cl
Determine the Missing Step of the Mechanism
Mechanism 7
CFCl3 →
Overall:
CFCl2 +
Cl
+
O3 →
ClO
+
O
Cl
ClO
+
→
Cl
O + CFCl3 + O3 →
O2
+
O2
CFCl2 + 2O2
+
Cl

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