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KS3 Chemistry
7F Simple ChemicalReactions
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7F Simple Chemical Reactions
Word equations
Reactions with oxygen
Chemical reactions everywhere
Summary activities
Reactions with acid
Contents
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What is a chemical reaction?
cooking rusting sticking
burning making metals living!
Can you think of any other chemical reactions?
Chemical reactions do not only happen in the laboratory.
Chemical reactions happen anywherethat new substances
are made:
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Reactants and products
The starting substances used in a reaction are reactants.
The new substances formed in a reaction are products.
Inachemicalreaction,oneormorenewsubstancesareformed.
The arrow means change into. In a chemical reaction,
all the reactants change intothe products.
It is difficult to reverse a chemical reaction and change the
products back into the reactants.
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More about chemical changes
Chemical changes are usually
difficult to reverse.
Magnesium burns in oxygen to form
magnesium oxide. It is not possible
to un-burn the magnesium once it
has been burnt.
Many reactions need energy to get them started.
Many reactions (like the burning of magnesium) give out
heat energyonce the reaction has started.
Heat energybeing given out is one sign of a chemical
reaction. What other signs of a chemical reaction are there?
magnesium oxideoxygenmagnesium
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7F Simple Chemical Reactions
Word equations
Reactions with oxygen
Chemical reactions everywhere
Summary activities
Reactions with acid
Contents
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magnesium+ acid
hydrogen
burningsplint
Many metals react with acids.
When this happens the metal
fizzes as bubbles are produced.
What do the bubbles mean?
A gasis produced.
How can you test to find out if the gas produced is hydrogen?
Place a burning splintnext to the mouth of test tube.Asqueaky pop as the gas ignites shows that hydrogen
is the gas produced in this reaction.
Test for hydrogen
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When a metal carbonate reacts with acid it fizzes and then
seems to disappear. The carbonate and the acid have
reacted and changed into a salt, waterand carbon dioxide.
When carbon dioxide gas is bubbled
through limewater, it turns thelimewatercloudy or milky white.
Test for carbon dioxide
a saltmetal
carbonateacid water
carbondioxide
Carbon dioxide can be tested for using
the limewater test.
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7F Simple Chemical Reactions
Word equations
Reactions with oxygen
Contents
Chemical reactions everywhere
Summary activities
Reactions with acid
Contents
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3. The names of the products.
A word equationis used as a quick, shorthand way of
writing a chemical reaction.
There are always three parts to a word equation:
1.The names of the reactants.
2. An arrow.
Word equations
What is the word equation for hydrogen reacting with oxygen
to form water?
wateroxygenhydrogen
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Substance Reactant or Product?
magnesium oxide
magnesium
copper oxide
copper
product
reactant
reactant
product
Reactant or product?
magnesiumoxide
magnesiumcopperoxide
copper
In this chemical reaction, which substances are the
reactants and which substances are products?
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What are the word equations for the following reactions?
2. Calcium hydroxide reacts with hydrochloric acid to form
calcium chloride and water.
3. Sodium reacts with hydrochloric acid to form sodiumchloride and hydrogen.
Write the word equations
magnesium oxideoxygen
calciumchloride
calciumhydroxide
hydrochloricacid
water
1. Magnesium burns brightly in oxygen to formmagnesium oxide.
magnesium
sodiumchloride
sodiumhydrochloric
acidhydrogen
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7F Simple Chemical Reactions
Word equations
Reactions with oxygen
Contents
Chemical reactions everywhere
Summary activities
Reactions with acid
Contents
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What is combustion?
Combustionis the scientific word for burning and is a
type of chemical reaction.
Combustion is the reaction when a substance burns and
reacts with oxygento produce heat and light energy.
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Burning has been an important source of energy since
primitive man and is still a hugely important process today.
Using combustion
How different would life be without combustion?
Burning fuel, like coal, petrol and natural gas, provides > 90%
of the energy needed for transport, factories and in the home.
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3.Methaneburns and forms carbon dioxide and water:
Equations for combustion
1.Coal(made from carbon) burns and forms carbon dioxide:
When substance burns and react with oxygen the new
substances formed are called oxides.
What are the word equations for these combustion reactions?
carbon
dioxideoxygencarbon
2.Hydrogenburns and forms dihydrogen oxide (i.e water!):
wateroxygenhydrogen
carbondioxide
oxygenmethane water
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Combustion of methane
The natural gas, methane, is often burnt for cooking.
Methane is made up of carbon and hydrogen.
What gas does methane react with when
it burns?
What substance will the carbon in methane
change into when it burns in oxygen?
What substance will the hydrogen in methane
change into when it burns in oxygen?
What is the word equation for the combustion of methane?
carbon
dioxideoxygenmethane water
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7F Simple Chemical Reactions
Acid reactions
Reactions with oxygen
Contents
Chemical reactions everywhere
Summary activities
Reactions with acid
Contents
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Glossary
carbon dioxideA gas that turns limewater cloudy.
chemical reactionA change in which new substancesare made and cannot easily be reversed.
combustionThe scientific word for burning which is thereaction of a substance with oxygen.
fuelA material that burns and generates useable energy.
hydrogenA gas that makes a lighted splint produce asqueaky pop.
productsThe new substances produced in a chemicalreaction and shown on the left of a word equation.
reactantsThe starting substances used in a chemicalreaction and shown on the right of a word equation.
word equationA summary of a chemical reaction.
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