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Identifying the Reactions Notes
Types of Chemical Reactions
 Chemists classify chemical reactions into 5 main types
 This helps to recognize patterns and predict the
products
 5 Types:
 Synthesis
 Decomposition
 Combustion
 Single Displacement
 Double Displacement
Synthesis Reactions
 Definition: Two or more substances react to form a
single substance

SIMPLER substances combine to form one COMPLEX
substance
 General Equation: A + B  AB
 To Identify: Has one product (a compound)
 Example: 2 Ca + O2  2 CaO
Synthesis Examples
 Two elements react to form one compound.

2 Mg+ O2  2 MgO
 Two compounds react to form one compound.

CaO + H2O  Ca(OH)2
 One compound and an element react to form one
compound.

2 SO2 + O2  2 SO3
Synthesis Analogy
 It is like a relationship or marriage
Decomposition Reactions
 Definition: A single compound breaks down
into two more simpler substances
 The reverse of a synthesis reaction
 General Equation: AB  A + B
 To Identify: Has one reactant (a compound)
 Example: H2CO3  H2O + CO2
Decomposition Examples
Metal carbonates produce metal oxides and carbon dioxide
1.

Na2CO3-->Na2O + CO2
Metal hydroxides produce metal oxides and water
2.

Ca(OH)2-->CaO + H2O
Metal chlorates produce metal chlorides and oxygen gas
3.

KClO3-->KCl + O2
Oxyacids produce water and a nonmetal oxide gas
4.

2HNO3-->H2O + N2O5
Metal oxides produce metals and oxygen gas
5.

Au2O3--> O2 + Au
Water can produce oxygen gas and hydrogen gas
6.

H2O--> H2 + O2
Decomposition Analogy
 It is like a breakup or divorce
Combustion Reactions
 Definition: A hydrocarbon reacts with oxygen to
produce water and carbon dioxide
 General Equation:
CxHy +O2  CO2 + H2O
 To Identify: O2 in reactants, CO2 and H2O in
products
 Example: CH4 + 2 O2  CO2 + 2 H2O
Single Displacement Reactions
 Definition: One element replaces a second
element in a compound
 General Equation: A + BC  AC + B
 To Identify: On each side of the equation,
you will see one element and one compound
 Example: Cu + 2AgNO3  Cu(NO3)2 + 2Ag
Single Displacement Examples
 Types of SR Reactions
 Metal replaces another metal

Mg + CuCl2  MgCl2 + Cu
 Metal replaces hydrogen

2 Li + H2O  H2 + Li2O
 Nonmetal replaces nonmetal

F2 + 2NaBr  2NaF + Br2
Single Displacement Reactions
 Whether displacement
will occur depends on
reactivity of elements
 Use activity series
 The more reactive
element can replace the
less reactive element
 If a less reactive element
tries to replace a more
reactive element then
no reaction
Single Displacement Analogy
 It is like getting divorced and finding a new spouse OR
breaking up and finding a new girlfriend/boyfriend
 Dancing analogy
Double Displacement Reactions
 Definition: Involves an exchange of negative ions
between two compounds
 Often take place in aqueous solutions and produce a
precipitate

A solid that is produced from liquid solution
 General Equation: AB + CD  AD + CB
 To Identify: On each side of the equation, you will
see two compounds
 Example: 2 NaOH + CuCl2  2 NaCl + Cu(OH)2
Double Displacement Analogy
 Dancing with two couples and you switch partners
Reactions Summary Table
Type of
Reaction
Reactants
Probable
Products
Generic Equation
Synthesis
2 or more
substances
One compound
A + B  AB
Decomposition
One compound
2 or more
substances
AB  A + B
Combustion
Hydrocarbon &
oxygen
CO2 + H2O
CxHy + O2  CO2 + H2O
•Metal &
compound
•New compound
& replaced metal
A + BX  AX + B
•Nonmetal &
compound
•New compound
& replaced
nonmetal
Single
Replacement
Double
Replacement
Two compounds
Two different
compounds
AX + BY  AY + BX