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Types of Chemical Reactions
Predicting Chemical Reactions
Types of Reactions
Many chemical
reactions have
defining
characteristics
which allow them
to be classified
as to type.
Types of Chemical Reactions
• The five types of chemical reactions in this
unit are:
 Synthesis (S)
 Decomposition (D)
 Single Displacement (SD)
 Double Displacement (DD)
 Combustion (C)
Synthesis Reactions
• Two or more substances combine to form
one substance.
The general form is A + X AX
Example:
Magnesium + oxygen  magnesium oxide
2Mg + O2  2MgO
Synthesis Reactions
• Synthesis reactions may also be called
composition or combination reactions.
Combination of elements
K + Cl2  KCl
ONLY One product will be formed
Decomposition Reactions
One substance reacts to form two or more
substances.
The breaking apart of a compound into
smaller elements or smaller compounds.
The general form is AX  A + X
Decomposition Reactions
There are 5 general Types of
Decomposition Reactions:
Decomposition of a binary compound
When the right energy is applied to a binary compound
it will break apart into its respective elements.
2NaCl  2Na + Cl2
Water can be decomposed by electrolysis.
2H2O  2H2 + O2
Decomposition Reactions
Types of Decomposition Reactions:
Decomposition of carbonates
When heated, carbonates break down to
form the metal oxide and carbon dioxide.
CaCO3  CaO + CO2
H2CO3  H2O + CO2
Decomposition Reactions
Types of decomposition reactions:
Decomposition of metallic hydroxide
Some metal hydroxides decompose into metal
oxides and water when heated.
Ca(OH)2  CaO + H2O
Note that this is the reverse of a similar
synthesis reaction.
Decomposition Reactions
Types of decomposition reactions:
Decomposition of metallic Chlorates
Metal chlorates decompose into the metal chlorides and
oxygen when heated.
2KClO3  2KCl + 3O2
Zn(ClO3)2  ZnCl2 + 3O2
– Some of these reactions are used in explosives.
Decomposition Reactions
Types of decomposition reactions:
Decomposition of Oxy-Acids and Bases
Oxy-acids decompose into
water and the non-metal oxide.
H2SO3  H2O + SO2
Ammonium hydroxide is actually ammonia gas
dissolved in water.
NH4OH  NH3 + H2O
Single Displacement Reactions
A metal will replace a metal ion in a compound.
The general form is A + BX  AX + B
A nonmetal will replace a nonmetal ion in a compound
The general form is Y + BX  BY + X
Cations replace Cations
Anions replace Anions
Single Displacement Reactions
Examples:
Ni + AgNO3 
• Nickel replaces the metallic ion Ag+.
• The silver becomes free silver and the
nickel becomes the nickel(II) ion.
Ni + AgNO3  Ag + Ni(NO3)2
Balance the equation:
Ni + 2AgNO3  2Ag + Ni(NO3)2
Double Displacement Reactions
Ions of two compounds exchange
places with each other.
The general form is
AX + BY  AY + BX
Cations replace Cations
Anions replace Anions
Double Displacement
NaOH + CuSO4 
The Na+ and Cu2+ switch places.
Na+ combines with SO42- to form
Na2SO4.
Cu2+ combines with OH- to form Cu(OH)2
NaOH + CuSO4  Na2SO4 + Cu(OH)2
Balanced
2NaOH + CuSO4  Na2SO4 + Cu(OH)2
Combustion Reaction
When hydrocarbon compounds are
burned in oxygen, the products are
water and carbon dioxide.
Methane, CH4, is natural gas.
CH4 + O2  CO2 + H2O
balanced
CH4 + 2O2  CO2 + 2H2O
Combustion Reactions
Combustion reactions involve light
and heat energy released.
Natural gas, propane, gasoline, etc. are
burned to produce heat energy.
Most of these hydrocarbon reactions
produce water and carbon dioxide.
Combustion Reactions
Show the combustion of Propane (C3H8)
C3H8 + O2  H2O + CO2
C3H8 + 5O2  4H2O + 3CO2
Practice
Classify each of the following as to type:
1)
H2 + Cl2  2HCl
 Synthesis
2) Ca + 2H2O  Ca(OH)2 + H2
 Single displacement
Practice
3) 2CO + O2  2CO2
 Synthesis and combustion
4) 2KClO3  2KCl + 3O2
 Decomposition
Practice
5) FeS + 2HCl  FeCl2 + H2S
 Double displacement
6) Zn + HCl  ?
 Single displacement
Products?
Zn + 2HCl  ZnCl2 + H2
Single Displacement Reactions
Not all single displacement reactions that
can be written actually happen.
The metal or non-metal must be more active
than the ion it is replacing.
It will depend upon the element’s Activity as
determined by the Activity Series (Sec. 3)
Single Displacement/
Replacement Reactions
An active nonmetal can replace a less
active nonmetal.
The halogen (F2, Cl2, Br2, I2) reactions
are good examples.
F2 is the most active and I2 is the least.
Cl2 +2 NaI  2 NaCl + I2