1. UNIT KINETICS
CROWE2009

2. 2.8.1 – Rate of reaction Connector:
a. recall the factors that influence the rate of chemical reaction, including concentration, temperature, pressure, surface area and catalysts
b. explain the changes in rate based on a qualitative understanding of collision theory
c. use, in a qualitative way, the Maxwell-Boltzmann model of the distribution of molecular energies to relate changes of concentration and temperature to the alteration in the rate of a reaction
d. demonstrate an understanding of the concept of activation energy and its qualitative relationship to the effect of temperature changes on the rate of reaction
Connector:
What three things must happen for a chemical reaction to take place?
Draw an energy level diagram for an exothermic reaction, then use arrows to show the activation energy, and the energy released by the reaction.
Explain the term activation energy.

3. Note: 1,2 & 3 are all necessary for a successful collision to occur
For a chemical reaction to happen:
The reacting particles have to collide
They have to have at least the Activation Energy
3. They have to have the correct orientation e.g HX + C=C
Activation energy
Energy released
Activation energy is the minimum amount of energy needed for a reaction to happen.
Note: 1,2 & 3 are all necessary for a successful collision to occur

4. The importance of orientation of collision

5. Factors affecting the rate of a reaction
Use collision theory to explain how the following factors can influence the rate of a reaction:
concentration
pressure
temperature
surface area
catalysts

6. Effect of concentration on rate of reaction
Effect of pressure on rate of reaction
An increase, increases the number of reactive particles and so increases the chance of effective collisions.

7. Effect of temperature on rate of reaction
Increasing the temperature:
Increases the kinetic energy of the particles so the particles move faster
this increases the number of collisions
also since the particles are moving faster, each collision will involve more energy, and so the chances of an effective/successful collision is increased.

8. Surface area and rate of reaction
Solids can only react at their surface, increasing the surface area of a solid increases the rate of reaction.
The smaller the pieces the greater the surface area

9. Catalysts
A catalyst is a substance that speeds up a chemical reaction.
A catalyst is not used up in the reaction it catalyses, and so can be used over and over again.
"A catalyst provides an alternative route for the reaction with a lower activation energy."

10. Reaction Profiles Potential energy
Note: when particles collide they slow down, stop then fly apart again, so KE converted to PE that then becomes KE ∆H
∆H = Enthalpy change of reaction
(Reaction coordinate)

11. The Maxwell-Boltzmann Distribution
This is a plot of the number of particles having each particular energy
The area under the curve is a measure of the total number of particles present.

12. The Maxwell-Boltzmann Distribution and activation energy

13. The Maxwell-Boltzmann Distribution and an increase in temperature

14. Summary exercise
Sketch a Maxwell-Boltzmann distribution curve to show the effect of using a catalyst.
Plus questions from work sheets or past papers