National 4
Unit 1
Chemical Reactions
Adapted from LCW
1
Chemical reactions revisited
Learning intention
A chemical reaction can be recognised by
 A new substance being made
 A change in colour
 A precipitate being formed
 Energy being given out
 Energy being used up
From the work you have already covered in S2 you already know that
when some chemicals touch each other they can react to make new
chemicals. This is called a chemical reaction.
Discuss with your partner what you remember from S2 about
chemical reactions – Make a spider diagram of what you both
remember.
If a chemical reaction happens a new substance is always made and
we might see:
 A change in colour - for example a rusting car



Adapted from LCW
A gas being made – for example a
rotting egg
A solid being made – for example milk
turning sour
Heat or light being given out or used up – for
example any kind of burning eg. coal, wood,
petrol, paper etc.
2
Note: Sometimes a solid is made when two clear solutions are
mixed. This solid has a special name – it is called a precipitate.
Your teacher may show you a DVD/Clip of chemical reactions
Experiment – Signs of a Chemical Reaction
Copy the table below..
Substances added what I saw
together
Was there a
chemical reaction?
(Yes/No)
Indigestion
powder + vinegar
Sulphuric acid +
copper
Sodium carbonate
+ cobalt chloride
Copper sulphate +
zinc
Sulphuric acid +
magnesium
Barium chloride +
sodium sulphate
Collect experiment card 1.20 and do the experiments. Fill in your
table as you go along.
Adapted from LCW
3
Answer these questions in sentences.
1. What is always made in a chemical reaction?
2. Give an example of
a)
a reaction where you might see a colour change.
b)
a reaction where you might notice a gas being made.
c)
a reaction where a solid forms from a liquid but not by
freezing.
d)
a reaction that gives out heat.
3. What is the special name for a solid that is made when two
solutions are mixed?
Extension
Try to think of chemical reactions that happen in the home where
the following happen ( think of the kitchen )
1. a colour change happens
2. a gas is made
3. heat is given out
Success task
Copy the following table
What is a chemical reaction?
Describe the signs of a chemical
reaction.
Describe an example for each
sign above.
Adapted from LCW
4
Telling if a gas has been made
Learning intention
 Describe how to tell if a gas is given off in a chemical
reaction
 Carry out an experiment safely by following instructions
Read
It is sometimes difficult to tell if a gas has been made in a reaction
but we know a gas has been made if:




We see bubbles made in a solution.
We can see it.
We can smell it.
We can use a test for it.
Write a heading and try the work below.
1. Make a list of that ways that we can tell if a gas has been made in
a reaction.
2. Copy the table below
What I heated
Adapted from LCW
what happened
chemical reaction?
5
You are going to complete a Practical skills Assessment for
this experiment so ensure that you
 Read the instructions carefully on the experiment
card.
 Be aware of safety features
Collect experiment card 1.21, do the experiments and fill
in your table. NB Use pyrex test tubes for heating.
Once complete,
 collect a Practical Skills assessment sheet and
fill it in.
 Complete the Self Assessment and Peer
Assessment sections of the Practical Skills
sheet.
Answer the following questions.
1. In the experiments above, how could you tell if a gas was being
made?
2. In one of your experiments the glowing splint relit. What does
this tell you about the gas that was made?
Success task
Practical Skills Assessment sheet has been completed and feedback
noted.
Adapted from LCW
6
Telling if there is an energy change
Learning intention
 Describe how to tell if heat is used up or given off
in a chemical reaction
Read
Sometimes the only way to tell if a chemical reaction has happened
is if there is an energy change.
Think! Can you name three different types of energy?
We can use a thermometer to check if heat is being made or used
up.
Write a heading and try the work below.
Copy the table below and fill it in as you do experiment 1.22.
What I added
together
Adapted from LCW
what happened
Chemical reaction?
(Yes/No)
7
Answer the following questions.
1. What type of energy has been made in these reactions?
2. Apart from the heat energy that is made, what other type of
energy is made when substances burn? (hint: think about sitting in a
room with no lights on but with a fire burning.)
Your teacher may show you a reaction where light is
given off in the reaction.
Answer the following questions.
1. What was done in the experiment?
2. What sign was there that a chemical reaction had
occurred?
3. Why should you not look directly at the reaction ?
Success task
Can you describe : An experiment where heat energy is given out
 An experiment where light energy is given out
Adapted from LCW
8
Everyday chemical reactions
Learning intention
 Describe whether a change is a chemical reaction or
a physical change
Read
Lots of changes take place in the world around us but it is not always
easy to decide whether these changes involve a chemical reaction or
not.
Think about freezing water. The water
changes in to ice but the ice is still water but
in the solid state. No new substance is formed
so freezing is not a chemical reaction. Boiling
water is also not a chemical reaction because the steam that is made
is just water. No new substance has been made.
Baking a cake, however, is a chemical reaction
because the substances we add together like
flour, butter, eggs, milk and sugar are changed
into new substances.
Answer the following questions.
1. Why is freezing or boiling water not a chemical reaction?
2. Is melting ice a chemical reaction? Explain your answer.
Adapted from LCW
9
Success task
Collect a set of cards and sort them into 2 piles
CHEMICAL REACTION
PHYSICAL CHANGE
Draw a table with these headings and write the answers into
the correct column.
Adapted from LCW
10
Word equations
Learning intention
 Be able to write word equations
Read
A short way to write down what happens in a chemical reaction is to
write it down as a word equation. A word equation is a simple way of
writing down what chemicals reacted to form products in the
reaction. There is set of rules for writing equations.
1. Draw an arrow in the middle of a line.
2. Write the names of the REACTANT chemicals we start with on
the left of the arrow separated by ‘+’ signs.
3. Write the names of the PRODUCT chemicals that are made on
the right of the arrow separated by ‘+’ signs.
REACTANTS
PRODUCTS
Example: When methane reacts with oxygen the new substances
that are made are water and carbon dioxide.
The word equation for this reaction will be:
Methane + oxygen
water + carbon
dioxide
The word equation must be on one line. Sometimes the names are
doubled up like carbon dioxide in the previous example to make sure
that the chemicals are on the correct sides of the arrow.
Remember:
 The chemicals that react at the start are called reactants
(methane and oxygen).
 The chemicals that are made or formed are called products
(water and carbon dioxide)
Adapted from LCW
11
Write a heading and try the work below.
1. What is a word equation?
2. What side of the arrow do the reactants go on?
3. What side of the arrow do the products go on?
Answer the following questions.
The sentences below tell you about some chemical reactions. Copy
each sentence and underneath it write a word equation for the
reaction. (The first one is done for you)
a) When calcium reacts with oxygen a new substance called calcium
oxide is made.
Calcium + oxygen
calcium oxide
b) When copper reacts with chlorine a new substance called copper
chloride is formed.
c) When iron reacts with fluorine a new substance called iron
fluoride is made.
d) Magnesium chloride is made when magnesium reacts with chlorine.
e) Sodium bromide is made when sodium reacts with bromine.
f) When aluminium is added to hydrochloric acid two new substances
are made. The new substances are called aluminium chloride and
hydrogen.
g) Sodium hydroxide and hydrogen are made if sodium is added to
water.
h) Petrol burns in oxygen to make carbon dioxide and water.
Adapted from LCW
12
i) Sugar burns in oxygen to give carbon dioxide and water.
j) If mercury oxide is heated it can be turned into mercury and
oxygen.
Success Task
Collect a set of word equation sort cards and follow the instructions
on the sheet.
Adapted from LCW
13