4.2 Types of Reactions
Synthesis Reaction: Two or more elements or compounds
combine to form a new product.
General:
A
+
B

C
Types of Syntheses:
(1) Direct union of two elements produces a binary
compound. **
i.e. Mg + O2  MgO
(2)
Metallic oxides and carbon dioxide produce carbonates.
i.e. CaO + CO2  CaCO3
(3)
Metallic oxides and water produce metallic hydroxides (a
base). **
i.e. CaO + H2O  Ca(OH)2
(4)
Non-metallic oxides and water produce an acid.
i.e. SO3 + H2O  H2SO4 **
N2O5 + H2O  HNO3
P2O5 + H2O  H3PO4
(5)
Binary salts and oxygen react to produce a chlorate.
i.e. KCl + O2  KClO3
Decomposition Reaction: A compound breaks down into
elements or simpler compounds. Opposite of a synthesis reaction.
You can recognize this because there is only ONE substance on
the left side of the arrow.
General:
C

A
+
B
Types of Decomposition:
(1) All binary compounds break down into their elements.
i.e. HgO  Hg + O2 **
(2)
All carbonates break down into the oxide and CO2
i.e. Na2CO3  Na2O + CO2
(3)
All chlorates break down into the binary salt (metal and nonmetal put together) and O2
i.e. Ba(ClO3)2  BaCl2 + O2
(4)
Metal hydroxides (bases) break down into the metal oxide
and water.
i.e. NaOH  NaO + H2O
(5)
When you see hydrogen bonded with a polyatomic ion (an
acid), it breaks into the non-metal oxide and water.
i.e. H2SO4  SO3 + H2O **
* Binary: two elements put together
** Binary salt: One is a metal; the other is a non-metal.