Types of Chemical
Reactions
Synthesis, Combustion, Decomposition and Replacement
You can think of atoms as people getting
together as couples...
Analogy
Chemical Reaction
One person
An ion or element
A couple
A compound
Switching partners
A replacement reaction
The Get Together…
Synthesis
Decomposition
Decomposition
Single Replacement Reactions
Single Replacement Reactions
Double Replacement Reaction
Double Replacement Reaction
Combustion
Combustion
How does this analogy break down?
People in Relationships
Chemical Reactions
People can switch partners whenever
they want
The ions or elements in a compound
“switch partners” according to rules
We usually just think about one
partner and one couple
In chemistry, we usually are dealing
with billions of particles reacting at
once
People don’t assume different states
of matter
In double replacement reactions,
there will be a change of state (a solid,
liquid, or gas is formed)
People aren’t swimming in water
Displacement reactions generally
happen in aqueous solutions
Let’s look at the
reactions in more detail
Synthesis
Decomposition
Single-Replacement
Double-Replacement
Combustion
Combustion
What are some types of
combustion you are familiar
with?
Every cell in your body is
carrying out combustion
Combustion
 Oxygen combines with a metal, non-metal, or compound
 Creates a metal oxide, non-metal oxide, or 2 or more oxides
 Releases energy – heat, light
 Can be a slower process too…
Synthesis
 2 or more reactants
combine to make a
product
A
B
AB
Decomposition
 A compound breaks down
into two or more
substances
Single Replacement
 A metal replaces a
hydrogen
 A metal replaces another
metal
 We use an activity series to
predict which metals are
“stronger” and can knock
out other metals from
compounds
Activity Series
The most active metals are at the
top. These will replace metals below
them.
The halogens are also listed in order
of most active at the top to least
active at the bottom.
More active elements replace less
active elements in single
replacement reactions
Single Replacement Examples
 2 AgNO3 + Cu  Cu(NO3)2 + 2 Ag
 Fe + Cu(NO3)2  Fe(NO3)2 + Cu
 Zn + 2HCL  ZnCl2 + H2
Double Replacement Reactions
 Produces a precipitate,
liquid or gas
 All four of the ions switch
partners
 Aqueous solution
Double Replacement Examples
 AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)
 CaCO3(aq) + 2 HCl(aq)  CaCl2(aq) + H2O(l) + CO2(g)
 HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
Steps to determine
type of reaction
Write the chemical equation
How to identify a
reaction
Be systematic – it will help you
identify the reaction type and the
products!
Determine what is happening in
the reaction
Use the table to identify the
type of reaction
Check your answer by
comparing the chemical
equation to the generic
equation
Example: Identifying a
reaction
How to identify a
reaction
Example:
Solid calcium oxide and carbon
dioxide gas react to produce solid
calcium carbonate
CaO (s) + CO2 (g) 
CaCO3 (s)
2 compounds are
reacting to form one
compound
This is a synthesis
reaction
A + B  AB
Summary
The main types of
reactions
 Combustion – reaction with
oxygen
 Synthesis – two compounds
or elements getting together
 Decomposition – One
compound splitting up
 Replacement – Another ion
moves in
Replacement Reactions:
2 types
 Single replacement – a
stronger cation steps in and
replaces a weaker anion
 Double replacement – 2
cations switch places,
forming a precipitate, a
liquid, or a gas
You try it!
 Work on these examples together in pairs.




Write the reaction
Balance the equation
Classify the reaction
Be prepared to present your results on the board!
 Magnesium and Hydrochloric acid form Magnesium Chloride and
Hydrogen
 Carbon Dioxide and Water form Carbonic Acid (H2CO3)
 Silver Nitrate and Sodium Chloride form Silver Chloride and
Sodium Nitrate
 Heating sodium bicarbonate (NaHCO3) releases water and
carbon dioxide and sodium carbonate
You try it!
 Magnesium and Hydrochloric acid form Magnesium Chloride
and Hydrogen:
 Mg + HCl  MgCl + H2 (skeleton equation)
 2Mg + 2HCl  2MgCl + H2 (balanced equation)
 Single replacement (reaction type)
 Carbon Dioxide and Water form Carbonic Acid (H2CO3):
 CO2 + H2O  H2CO3 (skeleton equation)
 CO2 + H2O  H2CO3 (it’s already balanced!)
 Synthesis (reaction type)
You try it!
 Silver Nitrate and Sodium Chloride form Silver Chloride and
Sodium Nitrate
 AgNO3 + NaCl  AgCl + NaNO3 (skeleton equation)
 AgNO3 + NaCl  AgCl + NaNO3 (already balanced)
 Double replacement (reaction type)
 Heating sodium bicarbonate releases water and carbon
dioxide and sodium carbonate
 NaHCO3  Na2CO3 + H2O + CO2 (skeleton equation)
 2NaHCO3  Na2CO3 + H2O + CO2 (balanced equation)
 Decomposition (reaction type)