1. The Collision Theory and Activation Energy
Explaining how and why factors affect reaction rates

2. The Maxwell-Boltzmann apparatus
Maxwell and Boltzmann performed an experiment to determine the kinetic energy distribution of atoms
Because all atoms of an element have roughly the same mass, the kinetic energy of identical atoms is determined by velocity (KE= ½mv2)

3. The Maxwell-Boltzmann apparatus
Maxwell and Boltzmann performed an experiment to determine the kinetic energy distribution of atoms
Because all atoms of an element have roughly the same mass, the kinetic energy of identical atoms is determined by velocity (KE= ½mv2)

4. The Maxwell-Boltzmann apparatus
Maxwell and Boltzmann performed an experiment to determine the kinetic energy distribution of atoms
Because all atoms of an element have roughly the same mass, the kinetic energy of identical atoms is determined by velocity (KE= ½mv2)

5. The Maxwell-Boltzmann distribution
The resulting disk looks like this:
Basically, if we plot the intensity of the dots on a graph we get a graph of fraction of atoms/molecules vs. kinetic energy:
Fraction of molecules
Kinetic energy 
Molecules hit disk first
Molecules hit disk last

6. Why is the graph skewed? This curve is characteristic of all molecules
The curve is elongated due to how atoms collide, and to the units of the graph
Recall all particles are in motion. An average speed will be reached.
The graph is skewed because 0 is the lower limit, but theoretically there is no upper limit
More than that the graph is skewed because the x-axis has units of energy not velocity
velocity KE
Same data, different axes. E.g. v=1, KE=1
v=2, KE=4
v=3, KE=9

7. Temperature and reaction rate
11/11/2018
By understanding the Maxwell-Boltzmann distribution, we can begin to understand the two reasons why an increase in temperature causes an increase in reaction rate
Read pg (starting at 18.7), answer questions on pg. 773 and …
Q- Look back at the five factors that affect reaction rates. Three of these factors can be (at least in part) explained by the collision theory. Identify the 3 factors and explain how the affect of each can be explained with reference to the collision theory

8. Temperature and reaction rate
11/11/2018
18.61 Rates are typically 2-3 times greater
18.62 Rate is proportional to the number of collisions per second among reactants
18.63 reactant orientation and activation energy
18.64 This happens because a larger fraction of the reactant molecules possess the minimum energy necessary to surpass Ea.
A- Ability to meet (molecules that are well mixed will have a greater chance of colliding)
Concentration of reactants (more molecules means more collisions)
Temperature (faster moving molecules means more collisions per unit of time). Plus…

9. Temperature and reaction rate
11/11/2018
Demonstrations: Mg + O2, H2 + O2
By increasing the temperature, a small number of molecules reach Ea. The reaction is exothermic, further increasing temperature and causing more molecules to reach Ea, etc.
Draw the M-B distribution for H2 + O2 before heat was applied. Show how heat affects the diagram.
Shift due to higher temperature
Fraction of molecules
Kinetic energy  Ea

10. Transition state theory
11/11/2018
Read remainder of 18.7 (pg. 756 – 757)
For more lessons, visit