Types of Chemical Reactions Notes
Types of Reactions
There are five main types of reactions:
Synthesis Reactions
Decomposition Reactions
Single-Replacement Reactions
Double-Replacement Reactions
Combustion Reactions
Synthesis Reaction
A synthesis reaction combines two or more reactants in to a single
product.
The general pattern for this reaction is:
A+B
AB
Examples of substances that often combine in synthesis reactions:
Metal + Nonmetal react to produce a salt compound.
CaCl2
Metal + Oxygen react to produce a metal oxide.
2 MgO
Ex: Ca + Cl2
Ex: 2 Mg + O2
Some Special Synthesis Reactions:
**A metal oxide and carbon dioxide react to produce a carbonate.
CaO + CO2 Ca(CO3)
**Binary salts and oxygen react to produce a chlorate.
2 KCl +3 O2  2 KClO3
**A metal oxide and water react to produce a metal hydroxide
CaO + H2O  Ca(OH)2
**Carbon and oxygen react to pproduce carbon dioxide.
**Non-metal oxides and water react to form an oxyacid.
Ex. SO2 + H2O  H2SO3
Decomposition Reaction
Decomposition reactions break down, or “decompose” a single reactant
into multiple products.
The general pattern for decomposition reactions:
AB  A + B
“AB” is always a compound
A and B (products) may be single elements or smaller compounds
Some common types of decomposition reactions:
Metal Oxides decompose (break down) to produce a metal + oxygen
Ex: 2 HgO  2 Hg + O2
Ternary acids (non-metal with hydrogen and oxygen) decompose (break
down) to produce a nonmetal oxide + water
Ex: H2CO3 
CO2 + H2O
Special Decomposition Reactions:
** Carbonates decompose (break down) to produce an oxide and carbon
dioxide.
Ex. CaCO3  CaO + CO2
**Chlorates decompose (break down) to produce a binary salt and
oxygen.
Ex. 2 Ba(ClO3)2  2 BaCl2+3 O2
Single-replacement Reaction
In a single-replacement reaction, a reactive element replaces a less
reactive element in a compound.
The general pattern for single-replacement reactions:
A + BX  B + AX
A = reactive element
The B in BX is less reactive than A.
Common single-replacement reactions:
*More active metal replaces the less active:
Zn + CuCl2  Cu + ZnCl2
*Metal replaces the H in an acid:
Mg + 2HCl  MgCl2 + H2
*More active halogen replaces less reactive:
Cl2 + 2NaBr  2NaCl + Br2
Single-replacement reactions occur because the element that does the
replacing is a more active element, based on its tendency to lose or gain
electrons.
To determine whether or not a single-replacement reaction will occur, refer
to the “activity series.” (t his is in the front cover of your notebook)
If the free element is above the other (in the compound) on the activity
series, a reaction will occur.
If the free element is below the other on the activity series, a reaction will
not occur.
Will a Reaction Occur?
Au (s) + NaCl (aq)  ?
Zn (s) + H2SO4  ?
Cl2 (g) + MgBr2  ?
Mg (s) + Ca(OH)2  ?
Double-Replacement Reactions
In a double-replacement reaction, two compounds switch partners.
The general pattern of this reaction:
AY + BX  AX + BY
Most double-replacement reactions take place when both reactants are
aqueous (dissolved in water).
When two aqueous compounds are mixed, and partners “swap,” a
precipitate is often formed.
Example:
Ex. Pb(NO3)2 + K2CrO4  PbCrO4 + 2 KNO3
Another example double-replacement reaction:
Ex. HCl + KOH  H2O + KCl
Follow this series of questions. When you can answer "yes" to a question,
then stop!
1) Does your reaction have oxygen as one of it's reactants and carbon
dioxide and water as products? If yes, then it's a combustion reaction
2) Does your reaction have two (or more) chemicals combining to form
one chemical? If yes, then it's a synthesis reaction
3) Does your reaction have one large molecule falling apart to make
several small ones? If yes, then it's a decomposition reaction
4) Does your reaction have any molecules that contain only one element?
If yes, then it's a single displacement reaction
5) If you haven't answered "yes" to any of the questions above, then
you've got a double displacement reaction