CHEMICAL REACTIONS
What happens to the atoms in a chemical reaction?
How can we tell if a reaction has occurred?
Where do raw materials come from?
How can we use reactions to make useful products?
Name
Class
Date
Teacher
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__________
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CORE BOOKLET 4
1
Using chemical reactions to make new
materials
Tick
You should:
Know that the chemical industry obtains raw materials
from the Earth, sea and air and that chemical reactions
are then used to change raw materials into useful
products, such as fuels, plastics, medicines, fertilisers,
metals etc.
Know that chemical reactions use up reactants and produce new
substances called products
Know that in a chemical reaction, atoms are rearranged but no
new atoms are produced nor are any atoms destroyed
Recognise that signs of a chemical change occurring may include
colour change, formation of a precipitate, gas evolution and
temperature change.
Know that reactions in which the temperature rises are
exothermic and that reactions in which the temperature falls
are endothermic
2
Summary sheets - Where do all our raw materials
come from.
This is a picture of the Earth’s
atmosphere taken from space. The
atmosphere is made up of a mixture
of gases. It can be cooled to a
liquid, then separated by a process
called fractional distillation. The
separated gases are used by chemists
as raw materials for new, more
useful substances. E.g nitrogen is
used to make fertilisers, oxygen in
medicine to aid breathing, argon in
welding and in light bulbs, helium in
weather balloons to name but a few.
This is a picture of the Earth.
Many raw materials come
from the Earth for example,
crude oil to make plastics,
fuels and medicines. Metals
such as iron, copper and
aluminium are also extracted
from the Earth for use in
steelmaking, wiring and food
cans respectively.
The sea is a great source of raw
materials for chemists. Sea water
itself is a solution of sodium
chloride (salt). It is therefore used
to make chlorine (water
purification), sodium hydroxide
(used as an alkali and to make
soap) and hydrogen (rocket fuel)
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What do chemists do with raw materials?
Chemists use chemical reactions to turn raw materials into new and more
useful substances.
During chemical reactions all that occurs is a
rearrangement of atoms. Each new arrangement of atoms represents a
new substance.
Chemical reactions can sometimes seem like magic because a new
substance can seem to appear out of nowhere. When this happens it
might be that for example; two colourless gases (that you can’t see) have
reacted together to form a liquid (which you can see).
At other times a substance may seem to have disappeared. This could be
when a solid has reacted with another substance to produce a colourless
gas.
To repeat; during a chemical reaction nothing is lost or gained! A
chemical reaction is simply a rearrangement of atoms. The reactants on
the left hand side of the equation will be the same mass as the products on
the right hand side of the equation. In Chemistry we refer to this as the
CONSERVATION OF MASS.
The Law of Conservation of Mass states that in a chemical reaction no mass is lost
or gained.
Take for example the reaction of hydrogen and oxygen gases to produce
water.
You can see that exactly the same atoms appear on the left hand side
as on the right hand. During the reaction there has simply been a
rearrangement of atoms. The reaction would be represented as:
2H2 (g) + O2(g)
2H2O(l)
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This means that for every two hydrogen molecules there will be one oxygen
molecule and that the two will react together to form two water molecules.
If there was a mass of 20g hydrogen reacting with 30g of oxygen then the
amount of water produced would be 50g.
Energy changes during chemical reactions
In physics you will have found out that there are a number of different
types of energy. All reactants contain a certain amount of CHEMICAL
ENERGY. During a chemical reaction particles collide together. Bonds
may be broken and new bonds made forming new products. As the
reaction occurs it will be accompanied by an energy change.
As an example, titanium metal is put into fireworks because
when it reacts with oxygen it creates silver sparks. This is because
chemical energy changes to heat and light energy when titanium and
oxygen particles collide and then react.
Reactions during which energy is given out to the surroundings are known
as EXOTHERMIC reactions. Most reactions are exothermic.
Some reactions take in energy from the surroundings. These reactions
are said to be ENDOTHERMIC.
A summary of what can happen to show that a chemical reaction has taken
place.
 A colour change occurs
 A gas is produced (bubbles are seen)
 The substance seems to have disappeared (usually if gases have formed and
escaped)
 A new substance seems to have appeared (usually if one of the starting
materials was a gas and a solid or liquid has been formed)
 Heat is given out (the reaction vessel heats up this is called an exothermic
reaction)
 Heat is taken in (the reaction vessel cools down, this is called an
endothermic reaction)
 Sound is given out
 Light is given out
 A precipitate forms (this occurs for example when two liquids react to form
an insoluble solid).
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Different Types of Chemical Reaction
Reaction type
Description
reaction type
Oxidation
reactions
Oxidation
reactions
occur
when
a
substance reacts with
and gains oxygen.
These reactions occur
when substances lose
oxygen.
Hydrogen reacts with
oxygen to form water.
Watch the teacher
demo of this reaction.
Ammonium
dichromate
loses
oxygen when heated.
Watch the video of
the
ammonium
dichromate volcano.
REDOX reactions
This
is
where
oxidation
and
reduction take place
at the same time.
Watch the teacher
demo
(fume
cupboard).
Be
prepared to jump!
Displacement
reactions
This is where a
reactive
element
pushes out a less
reactive element from
its compound
When magnesium and
copper oxide react,
the magnesium takes
copper’s oxygen. The
magnesium is oxidised
and the copper oxide
is reduced.
During the thermite
reaction
aluminium
displaces oxygen from
iron. Used in welding.
Reduction
reactions
of Example
Watch the video, Your observations
teacher demo or
do it yourself
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Watch the video of
the thermite reaction,
Endothermic
reactions
These are reactions
that take in heat from
their surroundings
Exothermic
reactions
These
are
reactions/changes
that give out heat to
their surroundings.
Decomposition
reactions
Thermal
decomposition
reactions
Watch teacher demo
These reactions occur
when one substance
breaks down to form
two
or
more
substances.
barium hydroxide and
ammonium thiocyanate
are mixed in a beaker.
Watch
it
freeze
water.
Wrap
wire
wool
cleaned in vinegar
around a thermometer
and
watch
the
temperature rise as it
oxidises.
Hydrogen
peroxide
will break down when
a catalyst is added to
make
water
and
oxygen.
These reactions occur
when one substance
breaks down with heat
to form two or more
substances.
If
green
copper
carbonate is heated it
will
lose
carbon
dioxide and become
black copper oxide.
Do
this
yourself.
Heat a small amount
of copper carbonate
on
a
combustion
spoon.
Note what
happens.
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Watch teacher demo
Do this yourself. You
can test using a
glowing splint to see if
it is oxygen being
produced. The black
manganese dioxide is
there to speed up the
decomposition. It is a
catalyst and does not
actually take part in
the reaction.
Neutralisation
reactions
Reversible
reactions
Metals on their own as
metals, metals oxides,
metal
hydroxides
(alkali’s)
or
metal
carbonates
can
remove the acidity
from an acid making it
neutral.
Some reactions occur
and then change back
to
the
starting
materials, they then
re-occur and so on.
The reaction moves
backwards
and
forwards,
is the
symbol for a reversible
reaction.
Bicarbonate of soda
removes the acidity
from
hydrochloric
acid.
The
‘Blue
experiment’
bottle
Do it yourself. Add
some
universal
indicator
to
2cm3
hydrochloric
acid.
Note colour, now add
sodium
bicarbonate
until
indicator
becomes green.
Add 20cm3 of the
methylene
blue
3
solution to 1cm of
the glucose solution in
a
conical
flask.
Watch out for a
colour change. Now
stopper and swirl the
flask.
Watch again.
Repeat several times.
Most of the time during a chemical reaction, more than one of the above happens at the same time. Burning is an
exothermic oxidation reaction for example. There are many other different types of chemical reactions, above are the
most common.
Thermite reaction website - http://video.google.com/videoplay?docid=-7231843493488769585
Volcano reaction website - http://video.google.com/videoplay?docid=-3710105662128434866
Endothermc reaction website - http://www.scs.sk.ca/cyber/elem/learningcommunity/sciences/chemistry30/curr_content/chem30/modules/module3/lesson1/labrxtypes.html
Note it is often the case that one chemical reaction can be described in more than one of the above ways. For
example, the above thermite reaction is also a REDOX reaction and it is EXOTHERMIC.
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Activity
Read the summary sheets (pages 3-5). Now answer the
questions below.
A 1. Write about the raw materials and useful substances they can
be turned into;
1. from the air.
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___________________________________________________
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2. from the sea
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2. From the Earth
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B1. Write out a balanced chemical equation for the reaction between
sulphur and oxygen in the space below. Use the following diagram to
help you with this.
2.
On the diagrams what do think the little black lines between
the atoms represent? ______________
3.
Write down the chemical formulae for the REACTANTS in
the above reaction;
4.
________
_________
Write down the chemical formula for the PRODUCT in the
above reaction; _______
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5.
What is the law of conservation of mass?
___________________________________________________
___________________________________________________
6.
i.
ii.
iii.
Write out the missing masses in the following equations:4Li +
O2
2Li2O
12g
6g
_____g
2Na +
2H2O
2NaOH
_____g
12g
15g
2K
Cl2
2KCl
55g
______g
+
30g
+
H2
5g
7. During a chemical reaction the reactants collide and energy is
taken in from the surroundings to break their bonds.
Energy is
given out when new bonds form and products are made.
i.
What do we call a chemical reaction during which the energy
taken
in
is
more
than
the
energy
given
out?
___________________________
ii.
What do we call a chemical reaction during which the energy
taken
in
is
less
than
the
___________________________
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energy
given
out?
C1. Sometimes during a chemical reaction it may look as though a
substance has disappeared. This is not possible, what could actually
have happened?
___________________________________________________
___________________________________________________
2. Sometimes during a chemical reaction it may look as though a
substance has appeared from nowhere. What has usually happened?
___________________________________________________
___________________________________________________
3.Write about four different observations that can be made to
indicate a chemical reaction is taking place;
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
D. Match up the following reactions with one of the reaction types
below. Some may link to more than one reaction type:
Each of
the reactions will come up at some point during the rest of your
course.
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During a reaction known as the Haber Process
nitrogen and hydrogen combine to form ammonia
so that the ammonia can be used to make
fertilisers. The trouble for the manufacturers
is that once ammonia forms it breaks back down
again to form nitrogen and hydrogen
Nitrogen + hydrogen
N2(g) +
ammonia
3H2(g)
THERMAL
DECOMPOSITION
Where one substance is heated so
that it breaks down into two or
more substances.
EXOTHERMIC
2NH3(g)
A reaction during which heat is given
out.
When the alkali sodium hydroxide reacts with
hydrochloric acid water as well as the neutral salt
sodium chloride is formed. At the same time, heat
is given out
NaOH(aq) + HCl(aq)
NaCl(aq) + H2O(l)
DISPLACEMENT
An element is ‘kicked out’ of its
compound by a more reactive
element.
Crude oil is made up of chains of molecules called
REDOX
A reaction during which as one
substance loses oxygen (reduction)
another substance gains oxygen
(oxidation)
hydrocarbons that look like this:
Shorter chains tend to be more useful than longer
chains. Manufacturers therefore take the long chain
hydrocarbons. They heat them up so that they
break down into shorter chains. This is called
cracking.
Once cracked, hydrocarbons are used as fuels as
when they react with oxygen, heat energy is
released that can heat water to steam. Steam turns
turbines, moving turbines create electricity.
nH-C + nO2 (g)
nCO2(g) + nH2O(l) + heat
During the extraction of iron form it’s ore (iron
oxide) oxygen is removed. Carbon in turn gains
oxygen. The oxygen is actually displaced by carbon
as carbon is more reactive than iron
Fe2O3(s) +
3C(g)
2Fe(s)
+
3CO(g)
Aluminium is extracted from its aluminium oxide ore
during a process called electrolysis. During
electrolysis Aluminium oxide loses oxygen to form
aluminium. Al2O3
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REVERSIBLE
As reactants form products the
products break back down again into
reactants.
COMBUSTION
Oxidation reactions during which
heat energy is released.
NEUTRALISATION
Where the acidity of a compound is
Removed by another compound to
make a product with a pH of 7.
REDUCTION
Where a substance loses oxygen.
OXIDATION
Where a substance reacts with and
gains oxygen
MINI PROJECT – WHAT CAUSES THE SILVER SPARKS IN A FIREWORK?
TASK – Your task is to use all that you’ve learnt in Chemistry so far to explain
how silver sparks are produced in a firework. You can tackle this task by
drawing an informative poster or by making and labelling a 3D model. Your
project will be awarded a grade A* to G (see grade descriptions below).
Projects will be judged by the Chemistry Department and a prize awarded to the
best one. Any information that has been cut and pasted from an internet
website will be ignored.
 Resource cards are available to help you, also if you type ‘chemistry of
fireworks’ onto google you’ll get lots of sites.
 Work your way through the grade ladder below to achieve your full
potential.
Gra
de
What to include to achieve grade
G
- A basic diagram of a firework.
- Mention that silver sparks are given out during chemical reactions.
F
- Mention that silver sparks are given out during the chemical
reaction between titanium and oxygen contained in the firework.
E
- Diagrams of titanium and oxygen particles
D
-An understanding that when a firework explodes a chemical reaction
occurs between titanium and oxygen and that this reaction is
exothermic.
-A mention about titanium and oxygen particles colliding during the
reaction.
- Write a word equation for the reaction!
C -A description of how a firework works.
- Use the word oxidation with regard to the titanium and oxygen
reaction.
-Word equations/chemical equations and particle diagrams to show
the combustion of titanium.
-Mention that the oxygen is provided in the firework by chemicals
called oxidisers as they decompose.
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B -Word and chemical equations to describe the decomposition of
substances such as potassium perchlorate used to provide oxygen for
the reaction.
-An explanation of energy changes that occur in the combustion of
titanium
- Appropriate use of key word such as oxidation, decomposition,
oxidising and reducing agent and exothermic.
- A discussion of surface area to describe how the rates of the
explosions are controlled in a firework.
A -An explanation of energy changes that can occur in a chemical
reaction (with particle diagrams) as a result of bond energies. Links
made between your explanation of energy changes and the energy
changes that occur during the combustion of titanium in a firework.
- Appropriate use of key word such as oxidation, decomposition,
oxidising, reducing agent and exothermic.
- Research on how charcoal is used to provide the initial energy to
initiate the reactions that occur in the firework.
A - Extra research carried out to explain (in your own words) how metal
* salts are used to provide different colours with an explanation
excited electron states (mega hard).
- Research on how the combustion of charcoal is used to provide the
energy to initiate the reactions that occur in the firework.
- Any other interesting facts that your teacher may not know such as
how the whistling sound is made.
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