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. Please write Ea ∆H ∆H = products – reactants
Activated Complex
∆H = products – reactants
Will give a positive value!
More energy went in than out!
ENDOTHERMIC!
Products Ea
Activation energy ∆H
Heat of Reaction
Potential Energy
Reactants
Progress of the Reaction

4. Please write Ea ∆H ∆H = products – reactants
Activated Complex Ea
∆H = products – reactants
Will give a negative value!
More energy went out than in!
EXOTHERMIC!
Reactants ∆H
Heat of Reaction
Potential Energy
Products
Progress of the Reaction

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

6. 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

7. 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

8. Factors affecting rxn rate:
Please write
Temperature:
↑ T = more molecules that are moving faster
= more likely that the collisions reach Ea
= higher rate of rxn (rxn occurs more often)
Concentration:
[↑] = collisions happen more often.
= more likely to have a successful collision.
= higher rate
Bond strength:
stronger bonds = higher Ea
= less likely to have a successful collision.
= slower rate
More factors next time …

9. 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 and reactants are similar.

10. 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.

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

12. Practice reading graphs
2, 3 (direct rxn means forward rxn),