1. Page 2 - List as many
factors as you can that
could speed up or slow
down a chemical reaction.
Below this list take some
notes from the video.

3. What does rate of reaction mean?
The speed of different chemical reactions varies hugely. Some reactions are very
fast and others are very slow.
The speed of a reaction is called the rate of the reaction.
What is the rate of these reactions?
rusting
slow
baking
fast
explosion
very fast

4. Different chemical reactions take place at
different speeds.
Very fast:
• explosion of a petrol-air mixture
• precipitation reactions
• fireworks going off
• coal burning
Moderately fast:
• reaction of metals or carbonates with dilute acids
Slow:
• rusting of iron in air
• reaction of magnesium with cold water
• oil forming
• silver tarnishing

5. Group Thought:
Why are some reactions faster than others?

6. Reactions, particles and collisions
Reactions take place when particles collide with a certain amount of energy.
The minimum amount of energy needed for the particles to react is called the
activation energy, and is different for each reaction.
The rate of a reaction depends on two things:
 the frequency of collisions between particles
 the energy with which particles collide.
If particles collide with less energy than the activation energy, they will not react.
The particles will just bounce off each other.

7. Changing the rate of reactions
Anything that increases the number of successful collisions between reactant particles will
speed up a reaction.
What factors affect the rate of reactions?
 increased temperature
 increased concentration of
dissolved reactants, and increased
pressure of gaseous reactants
 increased surface area of solid
reactants
 use of a catalyst
 use of light for some reactions ie.
photography or photosynthesis

8. Slower and slower!
Reactions do not proceed at a steady rate. They start off at a certain speed, then get
slower and slower until they stop.
As the reaction progresses, the concentration of reactants decreases.
This reduces the frequency of collisions between particles and so the reaction slows
down.
0%
25%
reactants
product
50%
75%
percentage completion of reaction
100%

11. GROUP ACTIVITY
Reaction was slow at the start
and then speeded up
Reaction was fast at the start
then slowed down.
Rate of reaction remained
constant throughout the
experiment.
Volume of
gas
produced
(ml)
Time (s)
1. Draw rate graphs for each scenario (use axis given)
2. Which graph would you expect to see for a rates of reaction
experiment?
3. How would you calculate the rate of the reaction?

12. Calculating rate of reaction from graphs
How can the rate of reaction be calculated from a graph?
70
hydrogen produced (cm3)
60
x
50
rate of reaction =
40
y
x
30
y
20
10
0
0
10
20
time (seconds)
30
40
50
The gradient of the graph is equal to the initial rate of reaction at that time
rate of reaction =
45 cm3
20 s
rate of reaction =
2.25 cm3/s

13. Now complete your worksheet!
Glue it on page 3 of your notebook
(flip page).