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 Activated Complex Products Potential Energy

Potential and Kinetic Energy Changes during a Collision Endothermic    Reactants Activated Complex Products Potential Energy

Potential and Kinetic Energy Changes during a Collision Endothermic    Reactants Activated Complex Products   max Potential Energy high  low

Potential and Kinetic Energy Changes during a Collision Endothermic    Reactants Activated Complex Products   max Potential Energy high  low Kinetic Energy

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

Pick the slow and fast reaction 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.

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

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

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

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

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

A potential energy diagram for this Mechanism has three humps 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)   highest A potential energy diagram for this Mechanism has three humps The 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.

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 + D   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   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   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   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   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   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   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   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 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction:   Intermediates: PE Reaction Path

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction:   Intermediates: PE Reaction Path

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: PE Reaction Path

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl PE Reaction Path

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = Ea (forward) =   Ea (reverse) = The enthalpy of Br The enthalpy of BrCl PE 800 600 400 200 Reaction Path

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) =   Ea (reverse) = The enthalpy of Br   The enthalpy of BrCl PE Reaction Path 800 600 400 200

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) =   Ea (reverse) = The enthalpy of Br   The enthalpy of BrCl PE Reaction Path 800 600 400 200

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) = 600 kJ   Ea (reverse) = The enthalpy of Br   The enthalpy of BrCl PE Reaction Path 800 600 400 200

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) = 600 kJ   Ea (reverse) = 400 kJ The enthalpy of Br   The enthalpy of BrCl PE Reaction Path 800 600 400 200

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) = 600 kJ   Ea (reverse) = 400 kJ The enthalpy of Br 300 kJ   The enthalpy of BrCl PE Reaction Path 800 600 400 200

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) = 600 kJ   Ea (reverse) = 400 kJ The enthalpy of Br 300 kJ   The enthalpy of BrCl 400 kJ PE Reaction Path 800 600 400 200

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 Overall Reaction: Intermediates:

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 Overall Reaction: Intermediates:

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

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

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD Overall: A + D + E → ADE  

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD Overall: A + D + E → ADE  

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD Overall: A + D + E → ADE   Put in step 3 so that you get the overall reaction

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD AD Overall: A + D + E → ADE   Put in AD to cancel

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD AD + → Overall: A + D + E → ADE   Put in AD to cancel

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD AD + E → Overall: A + D + E → ADE   Put in E

Mechanism 5 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → B + AD AD + E → ADE Overall: A + D + E → ADE   Put in ADE

Mechanism 6 Determine the Missing Step of the Mechanism C + D → CD   C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 6 Determine the Missing Step of the Mechanism C + D → CD   C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 6 Determine the Missing Step of the Mechanism C + D → CD   C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 6 Determine the Missing Step of the Mechanism C + D → CD   C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 6 Determine the Missing Step of the Mechanism → C C + D → CD   → C C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 6 Determine the Missing Step of the Mechanism → C C + D → CD   → C C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 6 Determine the Missing Step of the Mechanism A + B → C   A + B → C C + D → CD CD + E → ABE + D Overall: A + B + E → ABE  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl + O3 ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl + O3 → ClO + O2 ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl + O3 → ClO + O2 ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl + O3 → ClO + O2 ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl + O3 → ClO + O2 ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Mechanism 7 Determine the Missing Step of the Mechanism   CFCl3 → CFCl2 + Cl Cl + O3 → ClO + O2 ClO + O → Cl + O2 Overall: O + CFCl3 + O3 → CFCl2 + 2O2 + Cl  

Discussion Topic Define Reaction Mechanism Why is there a need of many steps? What number of particles do not need many steps? How to determine the rate-determining step? What step’s rate can be changed to change overall rate of reaction? What are intermediate and catalysts? How to add steps to find overall reaction How to find a missing steps from given steps and overall reaction? How to find formula of activated complex of a step?

Questions:

Reaction mechanism PE diagram

Reaction mechansim PE diagram

Reaction mechanism PE diagram

Reaction mechanism PE diagram

A potential energy diagram for this Mechanism has three humps 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)   highest A potential energy diagram for this Mechanism has three humps The slow step has the highest Ea PE Reaction Path Ea Ea(rev)

What do you need to know? 1. ΔH of each step 2. Ea (forward) of each step 3. Ea (reverse) of each step 4. The enthalpy (PE) of reactants, intermediates, products, activated complex, 5. Fastest, slowest step 6. Slowest, fastest moving particles based of KE

Mechanism 3 Step 1 Br2 → 2Br Step 2 Br + OCl2 → BrOCl + Cl Step 3 Br + Cl → BrCl Overall Reaction: Br2 + OCl2 → BrOCl + BrCl   Intermediates: Br Cl ΔH = 200 kJ Ea (forward) = 600 kJ   Ea (reverse) = 400 kJ The enthalpy of Br 300 kJ   The enthalpy of BrCl 400 kJ PE Reaction Path 800 600 400 200

Workbook page 30 Question 54-55