Decomposition reactions occur when a compound breaks down into simpler substances like elements or other compounds. There are three main types of decomposition reactions: thermal decomposition caused by heat, photo decomposition caused by light, and electric decomposition caused by an electric current. An example of a decomposition reaction is when water breaks down into hydrogen and oxygen gases.

1. Decomposition Reactions
Made By:-Ashutosh
Xth D
Roll-No:-6

2. Simple Reactions
Synthesis
(Combination)
Single
Replacement
Decomposition
Double
Replacement

3. A +
Synthesis
Decomposition
B
AB
AB
A + B
Single
AB + C
Replacement
A +CB
Double A B + C D
Replacement
AD + C B

4. Decomposition Reactions
• Decomposition reactions occur when a
compound breaks up into the elements or in a
few to simpler compounds
• 1 Reactant  Product + Product
• In general: AB  A + B
• Example: 2 H2O  2H2 + O2
• Example: 2 HgO 
2Hg + O2

5. Types of Decomposition
Reaction
• Thermal Decomposition Reaction
• Photo Decomposition Reaction
• Electric Decomposition Reaction

6. Thermal Decomposition
Reaction
• The Decomposition Reaction caused by
heat is called Thermal Decomposition
Reaction.

7. Photo Decomposition Reaction
• The decomposition reaction caused by
light is called photo decomposition
reaction.

8. Electric decomposition reaction
• The decomposition reaction caused by
electric current is called electric
decomposition reaction.

9. Decomposition Reactions
• Another view of a decomposition reaction:

10. Decomposition Exceptions
• Carbonates and chlorates are special case
decomposition reactions that do not go to the
elements. You should be able to recognize
these as decomposition only.
• Carbonates (CO32-) decompose to carbon
dioxide and a metal oxide
• Example: CaCO3  CO2 + CaO
• Chlorates (ClO3-) decompose to oxygen gas
and a metal chloride
• Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2

11. Decomposition Exceptions
• Ternary acids will tend to decompose to water
and the nonmetal oxide.
• Example: H2SO3  H2O + SO2
• There are other special cases, but we will not
explore those in this class