Chemical Equations
Define a
chemical
reaction
Describe and
explain why
mass is
conserved
11/03/2016
TBAT balance
symbol equations
KEYWORD: conservation of mass
STARTER:
Sodium + Chlorine  Sodium Chloride
What are the ‘reactants’ and ‘products’?
EXT: Write a word equation from this statement
“Hydrogen gas and oxygen gas react to form liquid water.”
What is a chemical reaction?
From your discussion,
write a definition in
your own words.
So, what do we mean by:
“Conservation of Mass”
Let’s look at a chemical reaction:

Hydrogen + Oxygen  Water

+

Does this show us that mass is conserved?
Do we have the same number of particles on each
side?
11/03/2016


Let’s add another molecule of Water
Hydrogen + Oxygen  Water


+

We now have the same number of Oxygen
particles on either side, but what about
Hydrogen?
How about now?

Hydrogen + Oxygen  Water

+

Chemical Reactions
In a chemical reaction…
 Bonds break
 New bonds form
 New substances are made


NB: We never change the mass though.
Think of baking a cake…..
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11/03/2016
REVIEW
In your own words, try to describe and explain in detail why
mass is conserved. You can use diagrams to support your
answer, but try and use the keywords below:
Conservation of mass
Define a
chemical
reaction
Reactant
Describe and
explain why
mass is
conserved
Product
Bonds
TBAT balance
symbol equations
11/03/2016
Testing for Carbon Dioxide
Limewater is calcium hydroxide solution,
Ca(OH)2. It forms calcium
carbonate,CaCO3, and water when it
reacts with carbon dioxide.
a Write a word equation for this
b Write a balanced symbol equation for
this
Calcium
+ carbon dioxide  calcium
+ water
hydroxide
carbonate
Ca(OH)2(aq) + CO2(g)  CaCO3(s) + H2O(l)
a Write a word equation for this
B Write a balanced symbol equation for this and
State symbols –
what are these?
It’s all a balancing act!
+


Write out the chemical formula for
each substance first
2 H2
+
O2

2H2O
Now add BIG NUMBERS at the front of the
substances to balance out the equations
H2 + Br2 → HBr
H2O2 → H2O + O2
Li + H2O → LiOH + H2
NaNO3 → NaNO2 + O2
Fe + O2 → Fe2O3
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H2 + Br2 → 2HBr
2H2O2 → 2H2O + O2
2Li + 2H2O → 2LiOH +H2
2NaNO3 → 2NaNO2 + O2
4Fe + 3O2 → 2Fe2O3
11/03/2016
REVIEW
(b) Write a balanced symbol equation for the reaction
between magnezium (Mg) and oxygen (O2) to form
magnesium oxide (MgO).
2Mg + O  2MgO
...................................................................................................................................
2
(1 mark)
Define a
chemical
reaction
Describe and
explain why
mass is
conserved
TBAT balance
symbol equations
11/03/2016
1)
CaF2 + Li2SO4  CaSO4 + LiF
2)
AlBr3 + K  KBr + Al
3)
Si(OH)4 + NaBr  SiBr4 + NaOH
4)
Li3PO4 + NaBr  Na3PO4 + LiBr
5)
CoBr3 + CaSO4  CaBr2 +
Co2(SO4)3
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1)
CaF2 + Li2SO4  CaSO4 + 2 LiF
2)
AlBr3 + 3 K  3 KBr + Al
3)
Li3PO4 + 3 NaBr  Na3PO4 + 3 LiBr
4)
Si(OH)4 + 4 NaBr  SiBr4 + 4 NaOH
5)
2 CoBr3 + 3 CaSO4 3 CaBr2 +
Co2(SO4)3
11/03/2016