1. Potential Energy Diagrams
Chemical Kinetics
Mrs. Kay

2. Review of Exothermic Reactants Ep is higher than Products Ep.
Now, we must consider the activation energy (the energy needed so that the reactants bonds will break and reform to make product)

3. Review of Endothermic Reactants Ep is lower than Products Ep.
Need to add more energy to the system for the forward reaction to take place.
Still need to consider activation energy

4. Activated Complex
Is the short-lived, unstable structure formed during a successful collision between reactant particles.
Old bonds of the reactants are in the process of breaking, and new products are forming
Ea is the minimum energy required for the activation complex to form and for a successful reaction to occur.

6. Fast and slow reactions
The smaller the activation energy, the faster the reaction will occur regardless if exothermic or endothermic.
If there is a large activation energy needed, that means that more energy (and therefore, time) is being used up for the successful collisions to take place.

7. Sample Problem
The following reaction has an activation energy of 120kJ and a ΔH of 113kJ.
2NO2  2NO + O2
Draw and label a potential energy (activation energy) diagram for this forward reaction.
Calculate the activation energy for the reverse reaction (if the reaction went backwards)

8. Another Problem
The following hypothetical reaction has an activation energy of 70kJ and a ΔH of -130kJ
A + B  C + D
Draw and label a potential energy diagram for the reaction
Calculate the activation energy for the reverse reaction.

9. Watch the following Flash
Review of what is occuring during a chemical reaction for both endothermic and exothermic.
KNOW THIS!!

10. Practice:
The following hypothetical reaction has an Ea of 120kJ and a ΔH of 80kJ
2a + B  2C + D
Draw and label a potential energy diagram for this reaction.
What type of reaction is this?
Calculate the activation energy for the reverse reaction.
Calculate the ΔH for the reverse reaction.

11. Analyze the activation energy diagram below.
What is the Ea for the forward reaction? For the reverse reaction?
What is the ΔH for the forward reaction? For the reverse reaction?
What is the energy of the activated complex?

12. Answer to #2
The activation energy (Ea) for the forward reaction is shown by (a): Ea (forward) = H (activated complex) - H (reactants) = = 300 kJ mol-1 The activation energy (Ea) for the reverse reaction is shown by (b): Ea (reverse) = H (activated complex) - H (products) = = 100 kJ mol-1 The enthalpy change for the reaction is shown by (c): H = H (products) - H (reactants) = = +200 kJ mol-1 for the forward and reverse reaction.