The speed at which a reaction
proceeds can be explained by using the collision theory.
What must first happen
for a chemical reaction to take place? Well......................!
Particles Must Collide
Particles don't Collide
No Reaction
Particles Must be moving fast enough
Particles Collide but are not moving fast enough
No Reaction
Fast moving Particles Collide
Reaction
1. The reacting particles must collide with each other
2. 'head
on'
3. with enough energy (known as the activation energy) to break existing bonds
4. and
with the correct
orientation to bring reactive
sites close together
5. to form new bonds
Relating The Theory To The Factors
Affecting Rate
More Collisions Increase The Rate of Reaction
The
rate of a Reaction Depends on Four Factors:
1. Concentration
- (or
PRESSURE FOR GASES)
2. Temperature
3. Catalyst
4. Size
of Particles
- (or
SURFACE AREA)
Rise
in Concentration - (or
PRESSURE FOR GASES) increases the the number of collisions
If the solution is made more concentrated (or pressure is increased in the case of gases), then the number of reacting particles are increased in a unit volume. Having more particles results in more
collisions, which leads to faster
a rate of reaction i.e. reaction
finishes in a quicker time.
Low
Concentration
High Concentration
Rise in Temperature
increases the number of collisions
Change in temperature alters the kinetic energy of reacting particles and hence the number
of successful collisions with enough energy to break existing bonds and make product particles.
The minimum energy needed to break
existing bonds is called the ACTIVATION ENERGY
(EA).
Increasing
the temperature of reacting particles results in:
a) increases the range
of kinetic energies;
b) increases the average
kinetic energy;
c) increases the number
of particles with more than the activation energy (see graphs below).
When the temperature of the reacting
particles is increased they all start
to move a lot faster. As a result
of their quikness they have more collisions.
