Kinetics

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Kinetics Lesson 4 PE Diagrams
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Potential Energy Diagrams   Kinetic Energy
(kJ)   Heat energy due to the motion of
particles. Simulation     Potential Energy or
Enthalpy (H).     ?H means change in enthalpy
It is also called the heat of the reaction
because it tells you how much heat or KE was
produced or consumed by the reaction.
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PE KE Total Energy is
constant   Conservation of Energy   PE KE
?H Reaction Type Decreases Increases -ve
exothermic Increases Decreases ve endothermi
c When PE (bond energy) decreases it is
converted into KE which increases. Remember that
KE is heat energy, so it gets hotter and it is
exothermic.
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Potential Energy Diagrams Exothermic Show the
change in potential energy or enthalpy during a
successful collision. Standard
Notation   H2 I2 ? 2HI 170 kJ   ?H
Notation   H2 I2 ? 2HI ?H -170
kJ   Both notations indicate an exothermic
reaction. The first indicates that 170 KJ of KE
are produced, while the second shows that the PE
decreases by 170 KJ.
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
KJ 1. An H2 and I2 approach each other
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 1. Reactants H2 and I2 approach each
other Reactants PE Reaction Path
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 2. They collide and become an Activated
Complex PE Reaction Path
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 2. They collide and become an Activated
Complex Unstable Reaction
Intermediate High PE Low KE Bonds
Break Form Reactant bonds break Activated
complex bonds form PE Reaction Path
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 3. New bonds form and products
separate PE R
eaction Path
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 3. New bonds form and products
separate
activated complex bonds break product
bonds form PE Reaction Path
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 3. New bonds form and products
separate Activated Complex
Reactants Products PE Reaction
Path
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 3. New bonds form and products
separate PE Reaction Path
Ea(for)
Ea(rev)
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Lets Explore the Potential Energy Changes during
a Single Collision H2 I2 ? 2HI 170
kJ 3. New bonds form and products
separate PE Reaction Path
Ea
Ea(rev)
?H -ve
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the activation energy is
200 kJ H2 I2 ? 2HI ?H -170
kJ     600   400 200 0            
 
PE (KJ)
Reaction Path
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the activation energy is
200 kJ H2 I2 ? 2HI ?H -170
kJ       600   reactants 400 200 0      
     
 
PE (KJ)
Reaction Path
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the activation energy is
200 kJ H2 I2 ? 2HI ?H -170
kJ       600   reactants
Ea 400 200 0            
 
PE (KJ)
Reaction Path
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the activation energy is
200 kJ H2 I2 ? 2HI ?H -170
kJ       600   reactants Ea 400
?H 200 0            
 
PE (KJ)
Reaction Path
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the activation energy is
200 kJ. H2 I2 ? 2HI ?H -170 kJ
      600   reactants Ea 400
?H 200 0            
 
PE (KJ)
Reaction Path
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Potential Energy Diagrams Endothermic   Standard
Notation   I2 Cl2 100 kJ ? 2ICl   ?H
Notation   I2 Cl2 ? 2ICl ?H 100
kJ   Both notations indicate an endothermic
reaction. The first indicates that 100 kJ of KE
are consumed, while the second shows that the PE
increases by 100 kJ.
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the energy of the
activated complex is 600 kJ.   I2 Cl2
100 KJ ? 2ICl        PE 600 400 200  
Reaction Path
 
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the energy of the
activated complex is 600 kJ.   I2 Cl2
100 KJ ? 2ICl      PE 600 400 200   R
eaction Path
 
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the energy of the
activated complex is 600 kJ.   I2 Cl2
100 KJ ? 2ICl        PE 600 400 200  
Reaction Path
 
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the energy of the
activated complex is 600 kJ.   I2 Cl2
100 KJ ? 2ICl        PE 600 400 200  
Reaction Path
 
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the energy of the
activated complex is 600 kJ.   I2 Cl2
100 KJ ? 2ICl        PE 600 400 2
00   Reaction Path
 
?H 100 KJ
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Draw the PE diagram if the enthalpy of the
reactants is 400 kJ and the energy of the
activated complex is 600 kJ.   I2 Cl2
100 KJ ? 2ICl      PE 600 400 20
0   Reaction Path
 
?H 100 KJ
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Draw the PE diagram if the enthalpy of the
reactants is 400 KJ and the energy of the
activated complex is 600 KJ.   I2 Cl2
100 KJ ? 2ICl        PE 600 400 20
0   Reaction Path
 
Ea
?H 100 KJ
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ         600     400     200    
 
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ           600     400     200    
 
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ         600     400     200    
 
Ea (rev) 400 kJ
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ         600     400     200    
 
Ea (rev) 400 kJ
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ           600   Ea (for)
200 kJ   400     200    
 
Ea (rev) 400 kJ
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ           600   Ea (for)
200 kJ   400     200    
 
Ea (rev) 400 kJ
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Draw the PE diagram if the enthalpy of the
products is 200 kJ, the Ea (for) 200 kJ, and Ea
(rev) 400 kJ           600   Ea (for)
200 kJ   400     200    
 
Ea (rev) 400 kJ
?H -200 kJ
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Exothermic Reaction
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Exothermic Reaction
Uncatalyzed reaction
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Exothermic Reaction
Uncatalyzed reaction
Catalyzed reaction
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Exothermic Reaction Reactants
Products
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Exothermic Reaction Reactants
Products stronger bonds
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Exothermic Reaction Downhill in PE KE is
produced
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Exothermic Reaction Downhill in PE KE is
produced
Ea(for)(uncat)
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Exothermic Reaction Downhill in PE KE is
produced
Ea(for)(uncat)
Ea(for)(cat)
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Exothermic Reaction Downhill in PE KE is
produced
Ea(for)(uncat)
Ea(for)(cat)
?H
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Exothermic Reaction Downhill in PE KE is
produced
Ea(for)(uncat)
Ea(for)(cat)
Ea(rev)(cat)
?H
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Exothermic Reaction Downhill in PE KE is
produced
Ea(for)(uncat)
Ea(rev)(uncat)
Ea(for)(cat)
Ea(rev)(cat)
?H
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PE(kJ) 500 400 300 200 100 0 reaction
path ?H forward ?H reverse Ea forward
uncat Ea reverse uncat Ea forward cat

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PE(kJ) 500 400 300 200 100 0 reaction
path ?H forward -300 kJ ?H reverse Ea
forward uncat Ea reverse uncat Ea forward
catalyzed

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PE(kJ) 500 400 300 200 100 0 reaction
path ?H forward -300 kJ ?H reverse 300
kJ Ea forward uncat Ea reverse uncat Ea
forward catalyzed

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PE(kJ) 500 400 300 200 100 0 reaction
path ?H forward -300 kJ ?H reverse 300
kJ Ea forward uncat 100 kJ Ea reverse
uncat Ea forward catalyzed

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PE(kJ) 500 400 300 200 100 0 reaction
path ?H forward -300 kJ ?H reverse 300
kJ Ea forward uncat 100 kJ Ea reverse
uncat 400 kJ Ea forward catalyzed

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PE(kJ) 500 400 300 200 100 0 reaction
path ?H forward -300 kJ ?H reverse 300
kJ Ea forward uncat 100 kJ Ea reverse
uncat 400 kJ Ea forward catalyzed 50 kJ

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PE(kJ) reaction path Slow rate
due to high Ea

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PE(kJ) reaction path The only way
to change the PE diagram is to add a catalyst.

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PE(kJ) reaction path The only way
to change the PE diagram is to add a
catalyst. More low energy collisions are
successful!

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PE(kJ) reaction path Slow rate
due to high Ea

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PE(kJ) 500 400 300 200 100 0 reaction
path Increasing the temperature does not change
the diagram. It gives more collisions the
required Ea and more are successful. Increasing
the concentration, pressure, and surface area
does not change the diagram.