1. A model for chemical kinetics
Collision model = built around the central idea that molecules must collide to react.
Activation energy, Ea, is the energy needed to disrupt molecules so they can form products.

2. 2BrNO(g) → 2NO(g) + Br2(g)
In this reaction two Br-N bonds must be broken and one Br-Br bond must be formed.
Breaking a Br-N requires energy which must come from somewhere.
The collision model proposes that the energy comes from the kinetic energies possessed by the molecules before the collision.
This KE is changed to PE as molecules are distorted during a collision to break bonds and rearrange the atoms into product molecules.

3. The arrangement of atoms at the top of the PE “hill” is called the activated complex, or transition state.
The rate of the reaction depends on the size of the activation energy, Ea.
Main point = a certain minimum energy is required to two BrNO molecules to “get over the hill” so that products can form.
This energy is furnished by the energy of the collision.
A collision between two BrNO molecules with small KE will not have enough energy to get over the barrier.
At a given temperature only a certain fraction of the collisions possess enough energy to result in product formation.

4. As temperature is increased, more collisions with required activation energy increases.
Rates of reactions are observed to increase with temperature.
Number of collisions having an energy greater than or equal to the activation energy is given by the expression:
Number of collisions with the activation energy =
(total number of collision)e-Ea/RT
The factor e-Ea/RT represents the fraction of collisions with energy Ea or greater at temperature, T.

5. Another requirement must also be met for reactants to collide successfully.
The relative orientation of reactants must allow formation of any new bonds necessary to produce products.

6. Determining Activation Energy
Graphically:
Plot ln(k) versus 1/T and using the slope to solve for Ea.

7. Or use the equation
The values of k1 and k2 can be measured at T1 and T2 and used to solve for Ea.

8. Catalysis
A catalyst is a substance that speeds up a reaction without being consumed itself.
How does a catalyst work?
A catalyst provides a new pathway with a lower activation energy.
A much larger fraction of collisions are effective at a given temperature, and the reaction rate is increased.