1. Five Factors that affect the Rate of Reaction
Learning Goals
be able to explain, using the collision theory, how the 5 factors affect reaction rates

2. Reaction Rates Chemical Reactions occur only when reactants collide:
In the proper orientation for bonds to form
With enough kinetic energy
(break old bonds and form new bonds) – reach Activation Energy
Particles in a chemical system are in constant motion with their Kinetic Energy (KE) proportional to their temperature.
**Explain orientation using 2 nitrosyl bromide molecules. - BrNO
EFFECTIVE
INEFFECTIVE collisions result in an elastic collision but no chemical rxn.

3. Activation Energy (Ea)
The minimum amount of energy that a reactant must have for a collision to be effective
Two main purposes:
Used to overcome the electrostatic repulsive forces between colliding reactants
Used to weaken the bonds of the reactants
‘Barrier’ to the reaction

4. Activation Complex (or Transition State)
New bonds are made before old bonds are broken
The activation complex is an unstable “Super Molecule” consisting of all reactants bonded together
Is very unstable with a high potential energy (the maximum in the change)

5. Recall

6. Five Factors that affect the Rate of Reaction
Temperature
Concentration/Pressure
Surface Area
Catalysts/Inhibitors
Chemical Nature of Reactants
Surface area and concentration – fall under the category of making molecules more available for collisions – shaking/stirring too.

7. Temperature
As the temperature increases the average Kinetic Energy increases.
More effective collisions = higher reaction rate
Temp increases, average kinetic energy increases, more reactants will have the E required to break bonds and form an activation complex. Increased KE also increases rate and force of collisions – increases probability the collisions will be effective.
Experimentally – reaction rates increase exponentially with temperature.

8. Temperature
Maxwell-Boltzmann Distribution
As the temperature is increased from T1 to T2 the KE of the particles increases and more particles achieve the activation energy F REACTION

9. Concentration & Surface Area
Concentration: As the number of particles increases the number of collisions increases (constant volume).
Surface Area: the more space for particles to react, the more likely they will collide.

10. Catalysts reduce the activation energy of the reaction.
Lower the activation energy = more particles will have the required amount of energy to react.
-catalysts provide an alternative pathway for the reaction that requires a lower Ea
-heterogeneous catalysts – catalyst is in a different state of matter than the reactants
-homogeneous catalysts – catalyst is in the same phase as the reactants (usually gas or liquid)

11. Nature of the Reactants
Rate depends on reactivity of reactants.
Ex. Au <<< less reactive than Na.