Types of chemical reactions
• Imagine that you are
baking some cookies at
home.
• You follow a recipe
• In the same way
chemists know that
elements and
compounds undergo
particular type of
chemical reactions
• How do you classify
elements?
• Chemical famillies
• Members react in a
similar way
How do we classify
compounds?
Ionic or molecular
- Have definite patterns
of chemical properties.
• Chemists use these
patterns to classify
groups of chemical
changes
• 4 categories
•
•
•
•
Synthesis
Decomposition
Single displacement
Double displacement
• Why is it useful to have any knowledge of of the
types of reactions?
• We can better understand experimental
observations.
• We can predict products of unknown reactions
Look at the reactants represented below, which reaction
involves elements as reactants? Which reaction involves
compounds as reactants?
Synthesis reaction
A synthesis reaction
involves the combination
smaller molecules
Decomposition reaction
A decomposition reaction
involves the breaking apart
of larger molecules
Recognizing the types of reactants is key to
identifying the reaction type
LETS US LOOK AT TWO OF THE REACTION
TYPES:SYNTHESIS AND DECOMPOSITION
Synthesis Reactions
• Involve the combination
of smaller atoms and
/or molecules into
larger molecules.
• They are also called
combination reactions
• General formula
• A + B
AB
• If you see two
elements as reactants,
you know the reaction
has to be a sysnthesis
reaction
• Most of these elements
are represented as
single atoms, but some
occur naturally as
diatomic molecules.
For example, hydrogen and
oxygen gases react to
produce water
hydrogen + oxygen
H2 + O2
Element
Diatomic molecule
Hydrogen
H2
Oxygen
O2
Nitrogen
N2
Fluorine
F2
Chlorine
Cl2
Bromine
Br2
iodine
I2
2H2 + O2
water
H2O
2H2O
• Synthesis reactions can also involve combinations of
small molecules.
• For example, when ammonia and hydrogen chloride
vapours combine, they form a white smoke as solid
particles of ammonium chloride are formed.
Hydrogen chloride + ammonia
ammonium chloride
HCl + NH3
NH4Cl
Similarly, combination of water and carbon dioxide
molecules
Synthesis reaction
CO2 + H2O
H2CO3(aq)
TYPICAL EXAMPLE , RAINWATER
Decomposition Reactions
• It involve the splitting of • Example, electrolysis of
a large molecule into
water uses electricity to
elements or smaller
split water molecules
molecules.
into their elements
water hydrogen + oxygen
• General formula
H2O
H 2 + O2
AB
A+ B
2H2O
2H2 + O2
• Sometimes it involves
large amounts of energy.
• Nitrogen triiodide
decomposes rapidly to
form the elements
nitrogen and iodine
nitrogen triiodide
• NI3
• 2NI3
nitrogen
+
iodine
N2 + I2
N2 + 3I2
• Can also involve the
production of two small
molecules from a large
molecule
• When ammonium nitrate
is heated to above 250oC,
it decomposes explosively
to form nitrous oxide and
water molecules
• NH4NO3 N2O + H2O
• NH4NO3 N2O + 2H2O
Single Displacement Reactions
Mg + AgNo3 Ag + Mg(NO3)2
• Are chemical changes
that involve an element
Mg + 2AgNO3 2Ag + Mg(NO3)2
and a compound as
reactants.
• One element displaces or
replaces another
element from the
compound.
• Example, when
magnesium ribbon is
placed in a solution of
silver nitrate
Example, when the element bromine is added to a solution
of calcium iodide
• the bromine displaces (or takes the place of) the iodide ion
•bromine + calcium iodide
•
Br2 + CaI2
iodine + calcium bromide
I2 + CaBr2