Download examples of chemical and physical reactions.

Chemical Reactions
1
What is a chemical reaction?
A chemical reaction is a reaction between 2 or more substances, where
the original substances change completely during the reaction, and at the
end new products are formed.
The substances that are present at the beginning of the reaction are
called _______________.
The substances that are present at the end of the reaction are called the
_____________.
Example: If we take a paper, the reactant is the paper. If we burn the
paper the reaction is burning. At the end of the reaction i.e. when the
paper completely burns, the product is ash. Ash is completely different
from the initial paper. Therefore, because there was a complete change
between the reactant and the product, the reaction is called a chemical
reaction.
A physical change is a change where the reactant doesn’t form a
completely new product.
For example, if a piece of paper is cut up into small pieces it still is paper.
This would be a physical change in the shape and size of the paper.
Chemical Change
Physical Change

The reaction cannot be reversed

The reaction can be reversed

A new product is formed

A new product is not formed
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
2
More examples of chemical and physical reactions.
Experiment:
Aim: To burn magnesium ribbon.
Apparatus: magnesium ribbon, tongs, Bunsen burner, matches, safety
glasses, watch glass.
Method:
1.
2.
3.
4.
5.
Cut a piece of magnesium ribbon and hold it in a tongs.
Observe its colour and shape
Burn over a lighted Bunsen burner
Observe the flame
Observe the reaction.
Results:
Initial colour _______________________________
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Shape ____________________________________
Colour of flame _____________________________
Final colour ________________________________
Shape ____________________________________
Precautions:
1. Wear protective safety glasses to protect your
eyes
2. wear a lapcoat or apron to protect your uniform
3. do not touch the fire
4. do not smell the burning magnesium
5. do not bring the tongs towards your body while holding hot
magnesium.
Conclusion: Was there a complete change between the reactant and the
product?
______________________________________________________
Do you think we can reverse the reaction?
_______________________________________________________
Do you think this was a physical or a chemical reaction? Why?
______________________________________________________
Equation: magnesium + oxygen  magnesium oxide.
Diagram:
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Answer: Tick the correct answer
Physical change
Chemical Change
Baking a cake
Striking a match
Making ice cubes
Dissolving salt in water
Burning some toast
Baking clay
Physical properties:
1) Has no colour or smell.
2) Has no effect on moist litmus paper or moist universal indicator paper
- it is neutral.
3) Burns with a characteristic 'pop'.
4) Hydrogen burns in air with a pale blue, almost invisible flame.
Specific test.
Hydrogen gas is recognized by the 'pop'
when it burns. The 'pop' is the sound of a
small explosion, hydrogen is extremely
flammable!
Experiment:
To produce hydrogen mix some metal example
magnesium with acid example hydrochloric
acid.
Metal + acid  hydrogen
gas.
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Metal + Acid  Salt + Hydrogen.
1.
Fill in the blanks. The following words might help you.
light
chemical
used up
heat
irreversible
new
Burning a match is a ________________ reaction.
It is an
________________ change.
The wood is ______________ and
__________ substances are made. Energy is given out as __________
and __________.
2.
Fill in the blanks. The following words might help you
pop
chemical
Hydrogen
acids
corroded
Some metals react with __________ to make hydrogen. We test for
______________ using a lighted splint. A __________ means it is
hydrogen. We say that the acid has _____________ the metal, because
the metal is used up in the _________________ reaction.
Combustion is a reaction that occurs when burning an organic material in
air. For example burning a paper, or burning wood etc. . . This releases a
gas called carbon dioxide.
Physical properties of carbon dioxide:
1. appearance – colourless , invisible gas
2. present in air (0.03%) – responsible for greenhouse effect
3. does not burn
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Producing carbon dioxide
1. heating a carbonate
limestone can be used here as the
carbonate.
2. breathing out – when we breathe out
(exhale) we release carbon dioxide.
If we breathe out in lime water, as
shown in this diagram, lime water
turns milky.
3. reacting a carbonate with an acid
Carbon dioxide turns lime water milky.
Complete these sentences:
All
carbonates
react
with
____________
to
produce
____________________ gas. We can test this gas by bubbling it into
___________ which turns ___________.
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Other reactions that release carbon dioxide gas.
This diagram shows what happens when yeast
reacts with sugar solution.
a.
This process is called ____________
____________.
Yeast use sugars to
produce energy. They also produce alcohol
and carbon dioxide.
b.
Carbon dioxide is given off during this
reaction.
c. The word equation for the above reaction is:
___________________________________________________
d. This reaction is used in the production of bread, alcohol (wine,
beer, etc)
Making cakes
Baking powder contains bicarbonate of soda
and a weak acid. When the powder gets wet,
the acid and the bicarbonate of soda react
together.
One of the products of the
reaction is carbon dioxide gas. This helps
cake mixture to rise.
Acid Rain
Marble stone (or limestone) is calcium carbonate. Carbonates dissolves in
acids. What do you know about acid rain? What happens to limestone in
acid rain?
_______________________________________________________
Fizzy drinks
What happens when you open a bottle of soft
drink or fizzy water that has been shaken? Do
you know that the gas that makes that ‘fizz’ is
carbon dioxide? In fact fizzy drinks are also
called carbonated drinks.
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
air.
8
The greenhouse effect
The carbon dioxide in the air has the
same effect as the glass in a
greenhouse. The carbon dioxide stops
some of the heat energy from the
Earth escaping, and the Earth stays
warm. This is called the Greenhouse
effect or Global warming. Scientists
think that too much carbon dioxide
will increase the temperature of the
Answer these questions.
1. Write some sentences about making of bread and alcohol.
2. What is making the Earth’s temperature getting hotter?
3. Write down the word equation of fermentation. What is the
importance of this reaction?
The Fire Triangle
Fire is a chemical reaction that requires three
main ingredients:
• fuel (carbon)
• oxygen
• heat
These three ingredients make up the fire
triangle. If any one is not present, a fire will
not burn.
Fuel generally is available in ample quantities in the forest. Fuel must
contain carbon. It comes from living or dead plant materials (organic
matter). Trees and branches lying on the ground are a major source of
fuel in a forest. Such fuel can accumulate gradually as trees in the stand
die.
Oxygen is present in the air. As oxygen is used up by fire, it is
replenished quickly by wind.
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Heat is needed to start and maintain a
fire. Heat can be supplied by nature
through lightning. People also supply a
heat source through misuse of matches,
campfires, trash fires, and cigarettes.
Once fire has started, it provides its
own heat source as it spreads.
BURNING CANDLES
What happens when a beaker is put over a burning
candle?
_______________________________
Why? _________________________________
Candle wax + oxygen
+ water + energy

carbon dioxide
Dangerous fires start when burning gets out of
control. Fire produces large amounts of energy as
heat and light. Firefighters sometimes have a
cylinder of oxygen on their backs, so they can
breathe in a burning building.
Preventing a fire using the fire triangle
What are you removing when you try to put off
a fire by:
a. using water?
_________________________
b. using a fire blanket?
_________________________
c.
switching
off
the
electricity
supply?_________________________
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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d. cutting down trees?
_________________________
e. using a CO2 fire extinguisher?
__________________________
f. using a powder fire extinguisher?
__________________________
Physical Properties

Oxygen is a colourless gas, without smell or taste,
 is slightly heavier than air,
 is sparingly soluble in water,
It is vital for most living organisms. It is obtained from air. There is 21
per cent by volume or 23 per cent by weight oxygen in the atmosphere.
Combined Oxygen also occurs




in water,
in vegetable and animal tissues,
in nearly all rocks and
in many minerals.
Oxygen occurs to a larger extent in the
earth's crust than any other element.
Testing for oxygen:
Oxygen rekindles a glowing
splint.
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Answer the following questions:
1. The chemical name for burning is __________________ . When
things burn, they react with ________________ gas in the air.
The products formed are called ______. _____________ gas
relights a _____________ splint.
2. You have burned magnesium in air. Remember that air is a mixture
of gases; so what do you think will happen if we burn magnesium in
pure oxygen gas?
________________________________________________
3. You are given three test tubes containing samples of hydrogen,
carbon dioxide and oxygen. What tests do you do to find out which
is which?
a. Hydrogen – ____________________________________
b. Carbon dioxide - _______________________________
c. Oxygen - _____________________________________
When a metal is attacked by water, air or acids in their environment, they
corrode. Corrosion results in the metal become weaker and brittle. The
corrosion of iron and steel is specifically called rusting due to the redbrown substance called rust that forms in the presence of water and
oxygen. The experiment below shows that an iron nail only rusts if
both water and oxygen are present:
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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How to prevent rusting
1. Paint or grease. This prevents water or oxygen reaching the iron.
However, this is only a temporary step since paint can flake off and
grease can be rubbed off quite easily. Bikes are often painted of greased
to prevent rust, since this is the cheapest method of prevention.
2. Plastic. Plastic is cheap and acts as a cover for the iron, for
instance, it stops water or oxygen reaching the metal surface. Garden
chairs are often made from iron coated in plastic.
3. Galvanising. This involves the iron been covered, usually in the form
of a paint, by zinc.
4. Chromium plating. Works for the same reason as galvanising. Car
bumpers are often chrome-plated.
Hydrogen filled balloons
Hydrogen was used to provide lift for the first balloons.
The hydrogen gas is
dangerous as it can
burn with the oxygen in
the
air
and
the
hydrogen filled balloon
can explode.
Modern airships are
filled with a gas called
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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helium, and they are a very safe way to travel as helium does not burn at
all!
Why did they use hydrogen to lift balloons?
____________________________________________________
Hydrogen is no longer used in balloons. Why?
____________________________________________________
Today Helium is used instead of Hydrogen. Why?
____________________________________________________
1. Chemical reactions make new materials. They are irreversible changes.
Which are chemical reactions and which are physical changes.
a) lighting a Bunsen burner _________________
b) salt disappearing as it is stirred into a beaker of water ___________
c) water droplets forming on a kitchen window __________________
d) green copper carbonate powder turning to black copper oxide when it is
heated strongly ___________________
2. Burning and rusting are similar because they are reactions where oxides
are formed. However, each reaction requires different things.
a) Complete these sentences.
i. For BURNING to take place, there must be a FUEL, OXYGEN and _________.
ii. For RUSTING to take place, there must be IRON, OXYGEN and _________.
3) Many changes take place everyday. Some of them are reversible and others
are not.
a) What is the meaning of the word reversible?
_______________________________________________________
b) Are reversible changes called physical or chemical changes?
_______________________________________________________
c) Which changes are reversible.
cooling water __________
boiling an egg _________
dissolving salt in water ________
baking bread _________
boiling water __________
burning a candle __________
4) A burning candle is floating on water and a beaker is placed over the burning
candle. What happens to the flame after a short time?
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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Why? ______________________________________________________
What happens to the water in the beaker?
____________________________________________________________
5) Fire-fighters use this knowledge to put out a fire.
Fill in the blanks:
Cool things down with water. This removes __________________.
Choke a fire with foam. This removes ___________________.
Let it burn out. This removes ____________________.
6) a) Give three examples of chemical reactions that take place in everyday life.
____________________________________________________________
b) Many metals react with acid giving off hydrogen gas.
i) Which metal and which acid are reacting together?
metal _______________ acid _______________
ii) How can you tell that a gas is given off?
___________________________________________________________
iii) Where is the gas collected?
___________________________________________________________
iv) Explain how you would check that this gas is hydrogen.
________________________________________________________
___________________________________________________________
7) Some materials can burn.
Underline the objects that can burn: paper, water, tree, iron, limestone,
coal, hydrogen
What gas is needed for a material to burn? ________________________
Where does this gas usually come from? ________________________
Mrs. J. Ebejer Grech B.Ed.(Hons.)
Chemical Reactions
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What two gases are produced when a wax candle burns?
______________________________________________________
Explain why a candle doesn’t burn unless it is lit by a match.
______________________________________________________
i) Write one similarity between rusting and burning.
_______________________________________________________
ii) Write one difference between rusting and burning.
______________________________________________________
8. Write down the equation for burning wax.
_____________________________________________________
9. These word equations show what happens when some chemicals are heated in
air. Complete the word equations below:
magnesium + oxygen  __________________
iron + __________________  iron oxide
zinc + oxygen  __________________
__________________ + oxygen  Sulphur dioxide
Sharon was doing some experiments to find out what acids can do to metals. She
was using magnesium, zinc and copper. She put a piece of each metal in a test
tube and added acid to them.
Two of the metals gave out bubbles of gas.
a) Which metals gave out bubbles of gas? ________________ ______
Sharon put a lighted splint at the mouth of the test tubes where gas was coming
out. She heard a loud ‘pop’.
b) What was the gas coming out? ______________________
c) Complete this word equation.
acid + _______________--> ________________
d) What did Sharon learn about copper?
______________________________________________________
Mrs. J. Ebejer Grech B.Ed.(Hons.)