2. Collision Theory
What is collision theory?
For molecules to react they
must first collide
In addition, they must be
the right orientation …
… and have
enough energy
cv cv

3. What affects reaction rate?
Temperature
Pressure
Concentration
Particle size
Catalyst
How fast a chemical reaction
goes is affected by many
factors.
List them …
What about enzymes?
Enzymes are biological
catalysts and for our purposes
will be considered the same
as chemical catalysts
How fast a chemical reaction
goes is affected by many
factors.
List them ...

4. Chemical reaction rates
Temperature
Why does sugar dissolve
in tea faster than water?
High Temp
Molecules have
more energy …
… fewer collisions
Low Temp
Molecules have
less energy …
… fewer collisions

5. As surface area
increases the rate
of reaction
generally increases
The particles
on the
surface can
react
When cut into
smaller pieces
the particles
on the inside
can react
Chemical reaction rates
Surface Area
Which one will dissolve first in
a cup of tea?

6. As the concentration of
reactants increases, so
does the likelihood that
reactant molecules will
collide …The fewer red particles
in a volume - the less
chance of a collision
The more red particles in
the same volume -
there is more chance of
a collision
Chemical reaction rates
Concentration
… the rate of
reaction increases

7. Chemical reaction rates
Pressure
What happens if you
increase the pressure in a
reaction?
Increase in Pressure
Molecules
are closer
together
Number of
collisions
increases
Rate of
reaction
increases

8. A substance that
increases the rate
of a reaction
without being
consumed in the
reaction
Chemical reaction rates
Catalysts
What is a catalyst?
Provide an alternative
pathway for reactions
… are biological catalysts (proteins)
that increase the rate of biochemical
reactions
Enzymes …

9. Chemical reaction rates
Look at the picture below …
A =
B =
reactants
products
Activation
energy
The energy
required for two
colliding
molecules to
react

10. Activation Energy
Our picture from before
can be redrawn …
Enthalpy
Extent of reaction
Activation energy (Ea)
enthalpy = energy

11. Activation Energy
Enthalpy
Extent of reaction
Ea
Energy of reactants
Energy of products
Because …
Energy of
reactants
Energy of
products
Exothermic
>
Energy
given out

12. Activation Energy
Enthalpy
Extent of reaction
Energy of reactants
Energy of productsEa
Because …
Energy of reactants Energy of products
Endothermic
>
Energy
taken in