Types of Chemical Reactions

Types of
Chemical Reactions
1. Synthesis Reactions
• A synthesis reaction occurs when two or more
simple substances combine to produce a more
complex substance.
• AKA: Combination reaction.
• The general equation for a synthesis is:
A + B  AB
• HINT: If there is only one product – it is likely a
Examples of Synthesis Reactions
• CO2 + H2O  H2CO3
• 4Fe + 3O2  2Fe2O3
• Li2O + H2O  2LiOH
2. Decomposition Reactions
• A decomposition reaction occurs when a complex
substance is broken down into two or more simpler
• Heat is often used to aid in decomposition reactions – these
reactions that employ heat are called thermal
• Decompositions and synthesis reactions are opposites.
• The general equation for a decomposition reaction is:
AB  A + B
• HINT: If there is only one reactant – it is likely a
decomposition reaction.
Examples of Decomposition Reactions:
• NH4NO3  N2O + 2H2O
• Ca(OH)2  CaO + H2O
• 2H2O2  2H2O + O2
3. Single Displacements
• A single displacement reaction occurs when a single
element takes the place of one of the elements in a
• AKA: Single Replacement
• The general equation for a single displacement
reaction is:
AB + Z  ZB + A
• Metals displace metals while nonmetals displace
• HINT: The single mysterious loner moves into town
and breaks up the happy couple!
Examples of Single Displacement Reactions
• Fe + CuSO4  FeSO4 + Cu
• 2K + MgO  K2O + Mg
• 2CuF + Ba  BaF2 + 2Cu
Not So Fast There…
• The lone element doesn’t always break up the couple!
We can use a tool called the activity series to predict if
the compound will stay together or break up.
• The activity series is a list of metals and hydrogen
that are arranged in order of reactivity.
Li K Ba Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Hg Ag Au
• The rule is that you can only be displaced by an
element that is to the left of you. This makes Lithium
the strongest and Gold the weakest.
• There is also a halogen activity series – it is used to
predict reactions with halides.
F Cl Br I
Using the Activity Series
You can use the activity series in three ways:
Straight Forward Single Displacements
Use the rule of “whoever is more to the left wins” to
see if there is a reaction or not.
Reactions with Acids
Straight forward Single Displacements
Reactions with Acids
Reactions with Water
Acids contain hydrogen (positive like the metals). If
you are to the left of hydrogen – you react and take its
place – if you are to the right – there is no reaction.
Reactions with Water
Only the first five elements (Li K Ba Ca Na) will react
with water. It will form a hydroxide and hydrogen gas.
4. Double Displacements
• A double displacement reaction always involves two
ionic compounds that switch partners with each other.
• Again, positive ions switch with positive ions (and/or
• The general equation for a double displacement
reaction is:
AB + XY  AY + XB
HINT: Two couples switch partners at the dance.
Examples of Double Displacement Reactions:
• Pb(NO3)2 + 2KI  PbI2 + 2KNO3
• Na2SO3 + 2HCl  2NaCl + H2SO3
• 2NaOH + H2SO4  2H2O + Na2SO4
Not So Fast There…Again!
There are three outcomes for a double
displacement reaction:
1) Precipitate – solid formed from two
Use the solubility rules.
2) Gas – some compounds form products
that break down further into gases.
3) Water – results from a neutralization
between an acid and a base.
5. Combustion Reaction
• A combustion reaction occurs when a
substance (the “fuel”) reacts very rapidly with
oxygen to form carbon dioxide and water.
• Combustion reactions release a good deal of
energy in a very short period of time.
• The general equation for a combustion
reaction is:
Fuel + O2  CO2 + H2O
• HINT: Something combines with oxygen to
produce carbon dioxide and water.
Incomplete Combustion
• If a combustion occurs at a lower
temperature, it may result in an
incomplete combustion.
• The products of an incomplete
combustion are water, carbon dioxide,
carbon monoxide and carbon (a solid
• The general equation is:
Fuel + O2  H2O + CO2 + CO + C