Kinetics Lesson 5 PE Diagrams Mechanisms

KineticsLesson 5

PE Diagrams Mechanisms

Potential and Kinetic Energy Changes during a CollisionEndothermic Reactants Activated Complex Products





Potential Energy


Potential Energy

Potential and Kinetic Energy Changes during a CollisionEndothermic Reactants Activated Complex Products max

Potential Energy high low


Potential Energy high low Kinetic Energy


Potential Energy high low Kinetic Energy

high min low


Potential Energy high low Uphill- endothermic! Kinetic Energy

high min low

Pick the slow and fast reaction


Ea Ea


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.

http://mc2.cchem.berkeley.edu/Java/molecules/index.html

Mechanism 1 .

HBr(g) + O2(g) → HOOBr(g) slow HBr(g) + HOOBr(g) → 2HOBr(g) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast

PE

Reaction Path

Mechanism 1 Cancel out identical formulas to get the overall equation.


PE

Reaction Path



PE

Reaction Path



PE

Reaction Path

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) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast

PE

Reaction Path

Mechanism 1 What is left is the overall reaction.


PE

Reaction Path

Mechanism 1 What is left is the overall reaction.

HBr(g) + O2(g) → HOOBr(g) slow HBr(g) + HOOBr(g) → 2HOBr(g) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast 4HBr(g) + O2(g) → 2H2O(g)+ 2Br2(g)

PE

Reaction Path

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) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast 4HBr(g) + O2(g) → 2H2O(g)+ 2Br2(g)

PE

Reaction Path

Mechanism 1 HBr(g) + O2(g) → HOOBr(g) slow HBr(g) + HOOBr(g) → 2HOBr(g) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast 4HBr(g) + O2(g) → 2H2O(g)+ 2Br2(g)

A potential energy diagram for this reaction might look like this.

PE

Reaction Path

Mechanism 1 HBr(g) + O2(g) → HOOBr(g) slow HBr(g) + HOOBr(g) → 2HOBr(g) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast 4HBr(g) + O2(g) → 2H2O(g)+ 2Br2(g)

A potential energy diagram for this reaction might look like this.

PE

Reaction Path

Mechanism 1

HBr(g) + O2(g) → HOOBr(g) slow HBr(g) + HOOBr(g) → 2HOBr(g) fast 2HOBr(g) +2HBr(g) → 2H2O(g)+ 2Br2(g) fast 4HBr(g) + O2(g) → 2H2O(g)+ 2Br2(g)

highestA potential energy diagram for this Mechanism has three humpsThe slow step has the highest Ea

PE

Reaction Path

Ea

Ea(rev)

The Rate Determining Step

The slowest step in the reaction mechanism is called the rate-determining 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.


C →→ C


C →→ C


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.


C →→ C


→ II →


C →→ C


→ II →

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: Intermediate:

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: Intermediate:

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: Intermediate: C

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: Intermediate: C

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: Intermediate: C CD

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: Intermediate: C CD

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: Catalyst: D Intermediate: C CD

Mechanism 2

1. A + B → C 2. C + D → CD 3. CD + E → ABE + D Overall Equation: A + B + E → ABE Catalyst: D Intermediate: C CD

Mechanism 3

Step 1 Br2 → 2BrStep 2 Br + OCl2 → BrOCl + ClStep 3 Br + Cl → BrCl

Overall Reaction: Intermediates:

PE

Reaction Path

Mechanism 3



PE

Reaction Path

Mechanism 3


Overall Reaction: Br2 + OCl2 → BrOCl + BrCl Intermediates:

PE

Reaction Path

Mechanism 3


Overall Reaction: Br2 + OCl2 → BrOCl + BrCl Intermediates: Br Cl

PE

Reaction Path

Mechanism 3



ΔH =Ea (forward) = Ea (reverse) =The enthalpy of BrThe enthalpy of BrCl

PE

Reaction Path

800

200

400

600

Mechanism 3



ΔH = 200 kJEa (forward) = Ea (reverse) =The enthalpy of Br The enthalpy of BrCl

PE

Reaction Path

800

200

400

600

Mechanism 3



ΔH = 200 kJEa (forward) = Ea (reverse) =The enthalpy of Br The enthalpy of BrCl

PE

Reaction Path

800

200

400

600

Mechanism 3



ΔH = 200 kJEa (forward) = 600 kJ Ea (reverse) =The enthalpy of Br The enthalpy of BrCl

PE

Reaction Path

800

200

400

600

Mechanism 3



ΔH = 200 kJEa (forward) = 600 kJ Ea (reverse) = 400 kJThe enthalpy of Br The enthalpy of BrCl

PE

Reaction Path

800

200

400

600

Mechanism 3



ΔH = 200 kJEa (forward) = 600 kJ Ea (reverse) = 400 kJThe enthalpy of Br 300 kJ The enthalpy of BrCl

PE

Reaction Path

800

200

400

600

Mechanism 3



ΔH = 200 kJEa (forward) = 600 kJ Ea (reverse) = 400 kJThe enthalpy of Br 300 kJ The enthalpy of BrCl 400 kJ

PE

Reaction Path

800

200

400

600

Mechanism 4

The following mechanism shows how chlorine-containing fluorocarbons destroy the ozone layer. Ozone is O3 and O 1. CFCl3 → CFCl2 + Cl 2. Cl + O3 → ClO + O2

3. ClO + O → Cl + O2


Mechanism 4


3. ClO + O → Cl + O2


Mechanism 4


3. ClO + O → Cl + O2

Overall Reaction: CFCl3 + O3 + O → CFCl2 + 2O2 + Cl Intermediates:

Mechanism 4


3. ClO + O → Cl + O2

Overall Reaction: CFCl3 + O3 + O → CFCl2 + 2O2+ Cl

Intermediates: Cl ClO

Determine the Missing Step of the Mechanism

Mechanism 5

A + B → C

C + D → B + AD

Overall: A + D + E → ADE


Mechanism 5

A + B → C

C + D → B + AD



Mechanism 5

A + B → C

C + D → B + AD


Put in step 3 so that you get the overall reaction


Mechanism 5

A + B → C

C + D → B + AD

AD Overall: A + D + E → ADE

Put in AD to cancel


Mechanism 5

A + B → C

C + D → B + AD

AD + → Overall: A + D + E → ADE

Put in AD to cancel


Mechanism 5

A + B → C

C + D → B + AD

AD + E → Overall: A + D + E → ADE

Put in E


Mechanism 5

A + B → C

C + D → B + AD

AD + E → ADE Overall: A + D + E → ADE

Put in ADE


Mechanism 6

C + D → CD

CD + E → ABE + D

Overall: A + B + E → ABE


Mechanism 6

C + D → CD

CD + E → ABE + D



Mechanism 6

C + D → CD

CD + E → ABE + D



Mechanism 6

C + D → CD

CD + E → ABE + D



Mechanism 6

→ C

C + D → CD

CD + E → ABE + D Overall: A + B + E → ABE


Mechanism 6

→ C

C + D → CD



Mechanism 6

A + B → C

C + D → CD



Mechanism 7

CFCl3 → CFCl2 + Cl

ClO + O → Cl + O2

Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl


Mechanism 7


ClO + O → Cl + O2



Mechanism 7


Cl

ClO + O → Cl + O2



Mechanism 7


Cl

ClO + O → Cl + O2



Mechanism 7


Cl + O3

ClO + O → Cl + O2



Mechanism 7


Cl + O3 → ClO + O2

ClO + O → Cl + O2



Mechanism 7


Cl + O3 → ClO + O2

ClO + O → Cl + O2



Mechanism 7


Cl + O3 → ClO + O2

ClO + O → Cl + O2



Mechanism 7


Cl + O3 → ClO + O2

ClO + O → Cl + O2



Mechanism 7


Cl + O3 → ClO + O2

ClO + O → Cl + O2


Date post:	19-Mar-2016
Category:	Documents
Upload:	mika
View:	41 times
Download:	0 times

Kinetics Lesson 5 PE Diagrams Mechanisms

Documents