1. Graphing ∆H
Chapter 5 P

2. Energy Diagrams Please write
Compare the potential energy of the reactants & products as the rxn occurs.
The reactants must have enough KE to overcome the repulsive forces between molecules.
When they collide with enough KE the reactants form a clump called the activated complex.
This is where the energy from the collision breaks the reactant bonds & forms the product bonds.
Activation energy is the minimum energy needed for a rxn to occur.

3. Not all collisions result in a rxn!
Please write
Not all collisions result in a rxn!
Activation Energy (Ea) = the minimum KE needed for the collisions to be effective
Activation Energy (EA)
ineffective collisions
Number of Particles
Not enough energy
Enough Energy
Kinetic Energy available during collisions 
effective collisions

4. Please write Ea ∆H ∆H = products – reactants = positive value!
Activated Complex
∆H = products – reactants
= positive value!
ENDOTHERMIC!
Products Ea
Activation energy ∆H
Heat of Reaction
Potential Energy
Reactants
Progress of the Reaction

5. Please write Ea ∆H ∆H = products – reactants = negative value!
Activated Complex Ea
∆H = products – reactants
= negative value!
EXOTHERMIC!
Reactants ∆H
Heat of Reaction
Potential Energy
Products
Progress of the Reaction

6. Slow, Faster & Spontaneous Reactions
Please write
Slow, Faster & Spontaneous Reactions
Rxns with high Ea It takes a lot of energy to get started, the rxn will begin slowly, or not at all.
Rxns with medium Ea. Will begin more easily & proceed more quickly.
Rxns with very low Ea. Spontaneous.
Potential Energy
Progress of the Reaction

7. Energy Diagram for a reversible reaction
Activated Complex
Ea(forward)
Reactants
Forward rxn
Ea(reverse)
–∆H(forward)
+∆H(reverse)
Potential Energy
Products of the forward reaction
Forward Reaction (Exothermic)
Reverse Reaction (Endothermic)
Progress of the Reaction

8. Conclusion from energy diagrams:
Please write
Conclusion from energy diagrams:
The Ea for the forward rxn is smaller. ∴the forward rxn occurs more often than the reverse. ∴ high concentration of products
The Ea for the forward & reverse rxns are similar.
∴both rxn occur with high frequency.
∴ concentration of products & reactants are similar.

9. Mechanism Energy Graphs
In a multi-step mechanism, each step will have an activation energy! The activation energy of several small steps is usually lower than a single activation energy would be, therefore these rxns are more common.

10. Photosyntheis: An extreme example of reaction mechanisms
Overall Reaction:
6CO2 + 6H2O  C6H12O6 + 6O2
Mechanism: