National 4
Unit 1
Rates of Reactions
Adapted from LCW Booklets
39
The Rate of chemical reactions
Learning intention
 Describe the rate of a chemical reaction as the
speed that the reactants are used up or the speed
that the products are made.
Read
Some reactions go faster than others. An
explosion is an extremely fast reaction,
making toast is a reaction that happens in
minutes while a car rusting or a body
rotting will take years. The rate of a
reaction is a measure of how fast or slow a
reaction proceeds.
Your teacher might demonstrate some
reactions for you (demo 1.24).
Write a short description of each reaction making sure you
include information about the rate of each reaction.
Adapted from LCW Booklets
40
Success task
Copy the table below and complete it by ticking the correct
boxes. Look at all the reactions before you start ticking the
boxes.
Chemical reaction
Reaction speed
slow
medium
fast
hydrogen exploding
a car rusting
a cake baking
coal burning
crude oil forming
firing caps in a toy gun
Adapted from LCW Booklets
41
Measuring the Rate of a Reaction
Learning intention
 Describe how to measure the rate of a chemical
reaction
The rate of a reaction can be measured by monitoring
how quickly a product is made or how quickly a reactant is
used up.
In S2 you completed some experiments where you
monitored the rates of some reactions and discovered
some things you could change to speed up these reactions.
Discuss with your partner what you remember about what
you learned in S2. Draw a spider diagram of what you
both can recall.
Reaction:
When Calcium Carbonate (marble chips) reacts with
hydrochloric acid the products formed are calcium
carbonate, water and carbon dioxide gas.
Think!
How would you measure the rate of this reaction?
How would you know if it was a fast or a slow reaction?
Discuss this with your partner and come up with an answer.
Adapted from LCW Booklets
42
Your teacher will now demonstrate how you can measure
the rate of this reaction.
Write a heading and try the work below.
1. What the reactants in the above reaction?
2. What are the products in the above reaction?
3. How was the rate of this reaction followed during the
reaction?
4. Write a word equation for the above reaction.
Extension
Try to think of another way that we could measure the rate
of this reaction (think of the marble chips !). Describe how
you would do this.
Adapted from LCW Booklets
43
Success task
Copy and complete the following sentence.
The rate of a reaction can be measured by the time
take for a _________ to be used up or a
__________ to form.
Adapted from LCW Booklets
44
Collision Theory of Reacting Particles
Learning intention
Describe how particle size affects the rate of a
reaction
For any reaction to occur the reactants must collide into
each other. They must be in contact to allow their atoms to
react and form new substances. This is called Collision
Theory.
Anything that is done in a reaction to help particles/atoms
to collide together will speed it up.
Your teacher will show you more about collision theory using
multimedia science school.
Write down what happens to the atoms when we change each of the
factors.
We will now investigate these 3 factors which can affect the speed
of a reaction.
Compare your experimental findings with the ones you have made
using multimedia science school.
Adapted from LCW Booklets
45
Particle size and the speed of reactions
Read
The speed of a reaction can be affected by using different
sizes of particles.
Your teacher will demonstrate some reactions for you




Burning
Burning
Burning
Burning
magnesium ribbon and magnesium powder.
a lump of coal and powdered coal
iron wire, steel wool and iron powder
normal sugar and icing sugar.
After watching the demonstration, copy and complete
the following paragraph using words from the word list.
Remember to read the paragraph before you start to
complete it.
WORD LIST – flame
faster
branch powder
Slowly
faster
A lump of coal or wood will burn _________ in air.
If we break up the lump, the reaction is _________.
Eg, wood shavings burn ________ than a __________
from a tree. If we use a __________. The reaction is
even faster, particularly when it is blown through a
________.
Adapted from LCW Booklets
46
Write a heading and try the work below.
Collect experiment card 1.26, and do the experiment.
Answer the following questions
1. What did you see that told you a chemical reaction
happened when you added the tablet to the acid?
2. How did you know which reaction was the fastest?
3. Make a list of two things you did to make sure the
two experiments were fair.
4. Copy and complete the sentence below.
The __________ the particles the __________ the reaction.
Adapted from LCW Booklets
47
Extension
1.Which will burn faster - small pieces of coal or large
lumps of coal?
1. Which will burn faster - a wooden log or
sawdust?
2. Which will cook faster - small potatoes
or large potatoes?
3. Dr Webster was running late and
wanted her barbecue to light quickly.
She had a choice between using
charcoal lumps or broken pieces of
charcoal she found at the bottom of
an old bag of charcoal. Which would
be the best to use and why?
4. Explain why it can be extremely dangerous to light a
match in an icing sugar factory but not so dangerous in a
sugar lump factory.
Adapted from LCW Booklets
48
Another Way of Following the Rate of Reactions
Using Graphs
Learning intention
Describe how a graph can inform us about the rate
of a reaction.
Read
So far we have been observing the rates of chemical
reactions by looking at how quickly products are formed.
This is what we did in S2. However, we can also collect data
from these reactions and line graphs can be drawn from the
data. These line graphs can also tell us information about
the rates of reactions.
Adapted from LCW Booklets
49
Effect of Particle Size: Following the Rate of
Reaction
Your teacher will now take you through a reaction where
we can follow the rate of the reaction by looking at a
graph of the results.
The experiment will be carried out with
 Marble chips
 Crushed marble chips
Time / Minutes
0
1
2
3
4
5
6
7
8
9
10
11
12
Adapted from LCW Booklets
Volume CO2
Chips
Volume of CO2
Powder
50
Success task
The results can then be used to draw a line graph.




You can draw both lines on the same graph
Draw each line a different colour.
Complete the Line Graph Success Criteria sheet
Answer the following questions
1. Which reaction was faster ?
2. what evidence from our graph tells us this ?
3. if the experiment was repeated with a lump of marble, would
the reaction be faster or slower ?
4. On your graph – in a different colour- draw on the line that
you think a lump of marble would produce.
Adapted from LCW Booklets
51
Investigating particle size: Indigestion Tablets
Learning intention
Describe how particle size affects the action of
indigestion tablets.
Read
Stomach acid is really hydrochloric acid. Its pH number is about 2.
You learned in S2 that indigestion can be caused by too much acid
being made in your stomach. This causes pain. The acid can be
'cancelled out' or as chemists called it "neutralised" by taking an
'antacid' tablet.
When the acid is being neutralised, its pH number rises towards 7.
We used the pH Sensormeter and a computer to compare how fast
the neutralisation was taking place using whole tablets and
powdered tablets.
Here is how it was set up:
Adapted from LCW Booklets
52
Success task
Now collect a graph of the results and discuss the
findings with your partner and write a conclusion for
these results in your jotter.
Adapted from LCW Booklets
53
Temperature and the speed of reactions
Learning intention
Describe how temperature affects the rate of a reaction.
Read
The temperature of chemicals can affect how fast they will
react together.
Watch your teacher demonstrate how to do the next
experiment.
measuring
cylinder
beaker
Hydrochloric
acid
Sodium thiosulphate
Paper with X drawn on it
The time for the reaction can be measured by timing how
long it takes for the X to disappear. Again the data
logger is being used to follow the reaction and produce a
graph)
1. What was the aim of the experiment (what were you
trying to find out)?
2. How did you measure the time for the reaction?
3. Draw a diagram of the experiment.
4. How did you change the temperatures?
5. Design a table for your results with two headings.
Adapted from LCW Booklets
54
6. What is your conclusion (what did you find out)?
7. Make a list of at three things you did to make sure that
the three experiments you did were fair.
8. Looking at the results on the graph, which reaction was
faster? Explain your answer.
Copy and complete the sentence below.
The ________ the temperature the __________ the reaction.
Discuss the following questions with your partner.
1. Where would food rot faster - in a fridge or in a
freezer? Explain your answer.
2. Where do plants grow faster - in a greenhouse or
outside? Explain your answer.
3. Sarah carried out an
experiment to compare
the speed of the
reaction of a metal
with some acid. Her
results are shown in
the table below.
Temperature(C) Time for all of
the metal to be
used up (sec)
0
78
20
45
40
23
60
10
a) Copy the table of results into your jotter.
b) Copy and complete the sentences below:
Adapted from LCW Booklets
55
As the temperature increases, the time for the metal to be
used up _________________.
As the temperature increases the reaction gets
____________________.
Adapted from LCW Booklets
56
Concentration and the speed of reactions
Learning intention
Describe how changing the concentration changes the rate of a
reaction.
Read
The concentration of a solution can change the speed of a
reaction. Remember back to the Solution topic you
completed recently. We found out that the unit of
concentration of a solution in chemistry is moles per litre
which is sometimes shortened to mol/l.
Question:
Which solution has the higher concentration; 0.1 mol/l or 1.0
mol/l?
PPA Experiment:
Rates of Reaction Experiment: Effect of concentration
Success task
PPA experiment completed accurately.
Adapted from LCW Booklets
57
Catalysts
Learning intention
Describe the effect that a catalyst has on the rate
of a chemical reaction.
Read
Another way to speed up a chemical reaction is to use a
chemical called a catalyst.
A catalyst speeds up a reaction but is not used up so it can
be used over and over again.
Your teacher may demonstrate (demo 1.29) a reaction
where a catalyst can be used to speed up a reaction to make
oxygen.
Glowing splint
Hydrogen
peroxide
Adapted from LCW Booklets
Glowing splint
Hydrogen
peroxide +
catalyst
58
Write a heading and answer the following questions.
1. What is the name of a chemical that can be used to speed
up a chemical reaction?
2. Why is it possible to use a catalyst more than once?
3. Copy a diagram of the demonstration that you saw and
add bubbles where you say them.
4. What happened to the glowing splint in the experiment
without the catalyst?
5. What happened to the glowing splint in the experiment
with the catalyst?
6. What does this tell you about the name of the gas that is
made in the reaction?
7. Which reaction made the gas the fastest?
8. Your teacher used 1g of catalyst in the second
experiment.
a) How much catalyst would there be after all of the
solution had reacted?
b) How could you separate the catalyst from the
solution to use it again?
9. Copy the sentences below.
Adapted from LCW Booklets
59
Use of catalysts
Catalysts are often used in motor car exhaust systems.
The part of the exhaust that contains the catalyst is
called a catalytic convertor. The catalytic convertor
changes harmful and poisonous gases into safer ones
that can go out into the air.
Success task
Draw a poster that shows how a chemical reaction can be speeded up
– use information from the multi media science schools programme
and your experimental conclusions.
Adapted from LCW Booklets
60