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All chemical reactions result in the formation of
new substances.
Since we can’t see atoms and molecules, we rely on
clues from the reaction to indicate whether a
chemical reaction has occurred.
These clues include (but are not limited to)
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H2
In a chemical reaction, atoms are rearranged to
make new substances.
There must be the same amount of atoms at the
beginning and at the end of the reaction…..the
atoms are just differently arranged.
ie. The total mass of the reactants must be the
same as the total mass of the products.
For this reason, all chemical equations must be
balanced….same amount of each element on
the product and the reactant side of an
equation.
+
Cl2
2 HCl
+
H
Cl
Cl
=
Total Mass
2(1.0) + 2(35.5)
73.0 g
=
H
H
Cl
Cl
H
H2
+
Cl2  HCl (unbalanced)
reactants
H
Cl
1.
2.
Total atoms
2H, 2 Cl
3.
4.
•
2
+
1
Cl2
reactants
H
1
2
H2
products
Cl
2

2 HCl (balanced)
products
2
2
2
There are five types of chemical reactions we
will talk about:
5.
=
Cl
H
•
Total Mass
2(36.5)
73.0 g
Cl
H
Cl
H
+
Total atoms
2 H, 2 Cl
Change in colour
Change in temperature (absorption or release of heat)
Release of energy as light
Production of gas
Formation of precipitate
Change in odour
Synthesis reactions
_____________ reactions
Single displacement reactions
________________ reactions
Combustion reactions
You need to be able to identify types of
reactions and predict their product(s)
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1. Synthesis: A + B  AB
Identify the type of reaction
Predict the product(s) using the type of reaction as a
model
Give the state of all reactants and products (see next
slide)
Balance it
1.
2.
2. Decomposition: AB  A + B
3.
3. Single displacement: A + BC  AC + B
4.
4. Double displacement: AB + CD  AD + CB
a) Neutralization: Acid(H) + Base(OH)  salt + H(OH)
b) Precipitation
c) Production of gas
5. Combustion: AB + oxygen  CO2 + H2O
An ELEMENT on its own –use the state on
periodic table
A COMPOUND:
•IONIC will always be solid (unless it is soluble in
water where it will be aqueous) – check solubility
rules
•MOLECULAR are usually gases
 Exception: H2O is liquid
•ACIDS and BASES are aqueous
 Any SOLUTION is aqueous
•
•
Synthesis reactions occur when two substances
(generally elements) combine and form a
compound. (Sometimes these are called
combination or addition reactions.)
reactant + reactant  1 product
Basically: A + B  AB
•
•
Example: 2H2 + O2  2H2O
Example: C + O2  CO2
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•Whenever a NEW ionic compound is formed,
use the ionic charges to determine the formula!
(ie. Criss-cross rule) and check its solubility to
determine its state as solid or aqueous
•Diatomic Molecules! (HOBrFINCl)

For example, Oxygen is O2 as an element.
Synthesis Reaction
2 Na
+

Cl2
Na
2 NaCl
Cl
Na+ Cl -
Cl
Cl - Na+
Na
General form: A
element or
compound
+
B
element or
compound

AB
compound
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Synthesis Reactions involving
oxides
OTHER EXAMPLES…
Elements that form ionic compounds:
Magnesium metal reacts with oxygen gas to
form magnesium oxide.
• 2Mg + O2  2MgO (metal oxide)
1.
2. Elements that form covalent compounds:
Nitrogen gas and oxygen gas join to form
dinitrogen monoxide.
• 2N2 + O2  2N2O (non-metal oxide)
 i)
Acidic oxides
react with oxygen to form
non-metallic oxides
 •Ex: The synthesis of carbon dioxide
 •Non-metals
 •Then,
SYNTHESIS REACTION (iron + sulphur):
http://www.youtube.com/watch?v=A5H6DVe5FAI
See pages 258 - 259
(c) McGraw Hill Ryerson 2007
when dissolved in water, nonmetallic oxides produce acidic solutions
 •(the oxyacid that corresponds to the
original non-metal is formed)
 •Ex: carbon dioxide reacts with water
Synthesis Reactions involving
oxides
 ii)
Basic oxides
 •Metalsreact with oxygen to form metallic
oxides
 Example: Sodium and oxygen
 •Then, when dissolved in water, metallic
oxides produce basic solutions
 (The
•
Here is another example of a synthesis reaction
metal combines with hydroxide)
Sodium oxide reacts with water
 Example:
•
•
•
•
Predict the products. Write and balance the
following synthesis reaction equations.
Sodium metal reacts with chlorine gas
Na(s) + Cl2(g) 
Solid Magnesium reacts with fluorine gas
Mg(s) + F2(g) 
Aluminum metal reacts with fluorine gas
Al(s) + F2(g) 
•
•
•
•
•
Decomposition reactions occur when a
compound breaks up into its elements or into a
few simpler compounds
1 Reactant  Product + Product
In general: AB  A + B
Example: 2 H2O  2H2 + O2
Example: 2 HgO  2Hg + O2
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Decomposition Reaction
•
Decomposition reaction
2 H2O
2 H2
H
O
+
Another view of a decomposition reaction:
O2
H H
O
H
+
H
O
O
H H
H
General form: AB
compound
A
+
B
two or more elements
or compounds
2. Covalent compounds may decompose into elements,
like the following:
•
 By running electricity through water, the water molecules
Carbonates (CO32-) decompose to carbon
dioxide and a metal oxide
•
decompose into hydrogen and oxygen gases.
 2H2O  2H2 + O2
Example: CaCO3 (s) CO2 (g) + CaO (s)
DECOMPOSITION REACTION:
http://www.youtube.com/watch?v=Nddwt
XEA_Ak
See page 260
(c) McGraw Hill Ryerson 2007
•
Chlorates (ClO3-) decompose to a metal
chloride and oxygen gas
•
Metal hydroxides break down into a metal
oxide and water
•
Example: 2 Al(ClO3)3 (s) 2 AlCl3 (s) + 9 O2 (g)
•
Example: Ca(OH)2  CaO (s) + H2O (l)
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Oxy acids break down to the non-metal
oxide (with the non-metal keeping its
charge) and water.
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Example: H2SO4 (aq)  SO3 (aq) + H2O (l)
•
•
•
Predict the products. Then, write and balance
the following decomposition reaction
equations:
Solid Lead (IV) oxide decomposes
PbO2(s) 
Aluminum nitride decomposes
AlN(s) 
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Read section 4.1 & 4.2
Pg 155 # 3-5
Pg 161 # 1, 2, 4, 8, 9
Identify the type of reaction for each of the
following synthesis or decomposition
reactions, and write the balanced equation:
N2(g) + O2(g)  Nitrogen monoxide
BaCO3(s) 
Co(s)+ S(s)  (make Co be +3)
NH3(g) + H2CO3(aq) 
NI3(s) 
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