Classifying Chemical
Reactions
• I CAN identify the four different types of
chemical reactions based on their
written equations.
• Chemical Reactions can be classified into
FOUR BASIC TYPES.
•
•
•

Composition (also called synthesis)
Decomposition
Single Replacement
Double Replacement
• A COMPOSITION REACTION, sometimes
known as a SYNTHESIS REACTION is a
reaction in which TWO OR MORE
SUBSTANCES react together to make a
LARGER, MORE COMPLEX
substance(s).
• The general form of the equations is:
•
A + B  AB
• Generally there is ONE PRODUCT;
sometimes TWO OR MORE PRODUCTS
can be formed, which makes this type
reaction harder to spot sometimes.
• Examples

2 H2 + O2  2 H2O

6 CO2 + 6 H2O  C6H12O2 + 6 O2

major product
minor product
• In a DECOMPOSITION, one substance
BREAKS APART to form TWO OR MORE
SIMPLE SUBSTANCES.
• The general form of the equations is:
•
AB

A
+
B
• While this type reaction is usually easy to spot,
sometimes there may be another reactant
associated and can make it confusing….BE
CAREFUL!
• Examples


2 KClO3  2 KCl + 3 O2
C6H12O6 + 6 O2  6 CO2 + 6 H2O
• A special type of decomposition reaction is
the COMBUSTION reaction.
• This type reaction generally involves a
HYDROCARBON (a compound composed
of CARBON and HYDROGEN) reacting
with OXYGEN.
• The products of this reaction are CARBON
DIOXIDE (CO2) and WATER.
• These reactions generally require the
INPUT OF ENERGY (heat) to initiate them
[ENDOTHERMIC] then proceed to
RELEASE ENERGY [EXOTHERMIC].
• Examples
• CH4
+
2 O2
• C 3H 8 + 5 O 2


CO2
3 CO2
+ 2 H 2O
+
4 H 2O
• In a SINGLE REPLACEMENT REACTION, a
FREE ELEMENT exchanges places with
another that is PART OF A COMPOUND.
• The element that was part of the compound is
dislodged as a FREE ELEMENT.
• Whether or not one element can replace another
is based on how REACTIVE the elements are:
– More reactive replace less reactive.
• The general form of the equation is:
A
•
BC 
+
AC
• Examples
K
Mg
+
LiBr
+

CaCl2
KBr
+
Li

MgCl2 + Ca
+
B
• In a DOUBLE REPLACEMENT REACTION, two
ELEMENTS in TWO DIFFERENT COMPOUNDS
exchange places with each other.
• In this type reaction elements simply TRADE
PLACES; LIKE replaces LIKE.
• In other words POSITIVE ions replace POSITIVE
and NEGATIVE ions replace NEGATIVE.
• The general form of the equations is:
AB
+
CD

AD
+
CB
Examples
• NaCl +
KI 
• MgI2
2 LiF
+
NaI
+
 2 LiI
KCl
+
MgF2
• 1.
H2 + O2 
• 2.
Ca +
• 3.
Al2O3
• 4.
Ca +
• 5.
Na2SO4 +
• 6.
P4 +
O2
• 7.
Na +
MgCl2 
H2O
H2O 

Ca(OH)2 +
Al +
H2
O2
Al2(SO4)3 
CaSO4
CaCl2 
CaSO4 +

P4O10
NaCl
+ Mg
+
Al
NaCl
• 8.
KMnO4 + Li2O

K2O + 2 LiMnO4
• 9.
CO2 + H2O 
C6H12O6
• 10.
KClO4 
+
• 11.
Mg +
• 12.
C2H4 +
KCl
Fe2O3 
O2

+
O2
Fe +
MgO
CO2 +
H2O
O2