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
synthesis.
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
substances.
• Heat is often used to aid in decomposition reactions – these
reactions that employ heat are called thermal
decompositions.
• 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
compound.
• AKA: Single Replacement
• The general equation for a single displacement
reaction is:
AB + Z  ZB + A
• Metals displace metals while nonmetals displace
nonmetals.
• 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:
1)
2)
3)
•
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
vice-versa).
• 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
liquids.
•
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
residue).
• The general equation is:
Fuel + O2  H2O + CO2 + CO + C
THE END