4.2 – 5.4: Types of Chemical
Reactions
Chemical Reactions
• There are millions of known chemical reactions!
• We can group these reactions by their reaction patterns,
making it easier to predict products of reactions.
• When predicting products for any reaction, follow these
steps:
Step 1: Identify reactant(s) (write formula with state!)
Step 2: Identify reaction type
Step 3: Predict the product(s) (formula and state) using the
rules for the specific reaction type
Step 4: Balance the equation
Chemical Reactions
 To predict states:
• An ELEMENT on its own – use the state on periodic table
• A COMPOUND:
• IONIC will always be solid
• MOLECULAR are usually gases
• Exception: H2O is liquid
• ACIDS and BASES are aqueous
• Any SOLUTION is aqueous
 Other important rules to remember:
• Whenever a NEW ionic compound is formed, use the
ionic charges to determine the formula!
• Diatomic Molecules!
• ie: the element chlorine is not Cl, it is always Cl2!
1. Synthesis Reactions
Definition: When two reactants combine to form one larger or
more complex product
Pattern: A + B  AB
a) Synthesis of Ionic Compounds (Metal and Non-Metal)
• Use ionic charges of the reactants to predict the product
Example: The reaction of magnesium with oxygen
1. Synthesis Reactions
b) Synthesis of Molecular Compounds (Non-Metals)
i) Reactions involving Hydrogen
• Although hydrogen is in Group 1, it is a non-metal and
usually forms molecular compounds.
• But, we still use ionic charges to predict the products.
Example: Synthesis of hydrogen chloride
1. Synthesis Reactions
ii) Reactions not involving Hydrogen
• Difficult to predict the products. They often depend on
the reaction conditions.
• Only way to identify the products is by chemical tests.
• For our purposes, simply combine the two nonmetals into the compound specified
Example: Synthesis of phosphorus tribromide
1. Synthesis Reactions
c) Synthesis Reactions involving oxides
i) Acidic oxides
• Non-metals react with oxygen to form non-metallic
oxides
• Ex: The synthesis of carbon dioxide
• Then, when dissolved in water, non-metallic oxides
produce acidic solutions
• (the oxyacid that corresponds to the original nonmetal is formed)
• Ex: carbon dioxide reacts with water
1. Synthesis Reactions
ii) Basic oxides
• Metals react with oxygen to form metallic oxides
Example: Sodium and oxygen
• Then, when dissolved in water, metallic oxides
produce basic solutions
(The metal combines with hydroxide)
Example: Sodium oxide reacts with water
1. Synthesis Reactions
Practice!
a) Show the synthesis of calcium oxide. Then, show the
reaction when it reacts with water.
b) Show the 2 step synthesis of sulfuric acid. (Formed
when sulfur trioxide reacts with water).
2. Decomposition Reactions
Definition: A large or more complex compound breaks
down into two (or more) simpler products.
Usually requires heat or energy (Δ)
Pattern: AB
Δ
→
A + B
a) Simple Ionic or Molecular Compounds
• The compound breaks down into its elements
Example: Decomposition of potassium chloride
Example: Decomposition of ammonia
2. Decomposition Reactions
b) Complex Compounds
• A compound breaks down into two simpler compounds
• Often difficult to predict, except:
• Carbonates decompose into a metal oxide and CO2
Example: The decomposition of calcium carbonate
Example: The decomposition of lithium carbonate
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3. Single Displacement Reactions
Definition: When one element displaces/replaces another
element in a compound.
Pattern:
A + BC → AC + B
A + BC → BA + C
if A is a metal
If A is a non-metal
Example: Zinc reacts with copper (II) sulfate solution
Example: Bromine reacts with magnesium oxide solution
3. Single Displacement Reactions
The Activity Series of Metals
 Not all single displacement reactions “on paper” actually
occur. It depends on the reactivity of the two metals.
 The Activity Series is a list of metals and their reactivity.
(see handout)
The most reactive metals are on top
An element (on its own) can only displace another
element (in a compound) if it is MORE REACTIVE
(higher on the activity series)
Otherwise, no reaction occurs!
The farther apart two elements are, the quicker the
reaction
3. Single Displacement Reactions
3. Single Displacement Reactions
a) Reactions Involving a Metal and an Ionic Compound
 Use the activity series to determine if a reaction occurs
• If reaction occurs, write the products
• If no reaction occurs, just write NO REACTION.
Example: Magnesium metal is placed in a solution of copper (II)
sulfate
Example: Lead is placed in a zinc nitrate solution
3. Single Displacement Reactions
b) Reactions Involving a Metal and Water or Acid (H+)
 Same idea as above: Hydrogen is also on the activity series
**Treat acids and water as if they are ionic compounds
(with an H+)
H2O =
H+ OHH2SO4 = H+ H+ SO4 2Example: Lithium is added to sulfuric acid
Example: Sodium is added to water
3. Single Displacement Reactions
c) Reactions Involving a Non-Metal
• Halogens have their own activity series – follows group
pattern
Example: The reaction of chlorine and potassium iodide
solution
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4. Double Displacement Reactions
Definition: When elements in two compounds displace each
other/trade places, producing two new compounds.
Pattern: AB + CD  AD + CB
** Like replaces like (metals switch places)
4. Double Displacement Reactions
Recall: Solubility
• Solution - HOMOGENEOUS mixture of 2 or more
substances (ie: salt water)
• Solute – the substance that dissolves IN a solvent (salt)
• Solvent – the substance that dissolves the solute (water)
• Solubility – the quantity of solute that dissolves in a given
quantity of solvent at a given temperature
• (aq) – aqueous – is soluble in solution
• (s) - solid precipitate – is NOT soluble in solution
4. Double Displacement Reactions
a) Precipitation Reactions (Two ionic compounds)
 Reactions between two compounds don’t ALWAYS happen. It
depends on their solubility.
 If a precipitate forms, a reaction occurs, because one of the
new compounds is not soluble in the solution of the other
compound.
 If no precipitate forms, there is no reaction
How do we determine if a precipitate forms? USE the
SOLUBILITY chart (see handout)
Practice: Determine if the following compounds are soluble
(aq) or insoluble (s) in water:
a) AgCl
b) MgCl2
c) Na2CO3
d) BaSO
4. Double Displacement Reactions
Example: Solutions of potassium chloride and silver nitrate are
combined.
Example: Solutions of potassium sulfate and iron (III) chloride
are combined.
4. Double Displacement Reactions
b) Reactions that Produce a Gas
 Double displacement reactions involving an acid can
produce gases. Gases may be produced in two ways:
1. Directly
Example – a metal sulfide will produce hydrogen sulfide gas
Gases formed:
Sulfides  H2S
Carbonates  CO2
Sulfites  SO2
2. Indirectly
 an unstable product can decompose into water and a gas
Example: A carbonate
Example: A sulfite
4. Double Displacement Reactions
c) Neutralization Reactions
i) With a hydroxide compound
Pattern: Acid + base → Salt + water
• Acid has H+, Base has OH- - these ions combine to
form HOH (H2O)
• Other cation and anion combine to form a SALT
(ionic compound)
Example: hydrochloric acid and sodium hydroxide
4. Double Displacement Reactions
c) Neutralization Reactions
ii) With a carbonate compound
Pattern: Acid + carbonate → ionic compound + water +
carbon dioxide
Example: Calcium carbonate reacts with sulfuric acid to produce carbonic acid:
But, carbonic acid immediately decomposes into water and carbon dioxide
The chemical equation for the net reaction of calcium carbonate and sulfuric
acid is:
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Self Quiz: Page 183 #1-17
REVIEW page 184 #1-20, 22, 29, 33, 48, 50, 54, 57, 63, 71
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5. Combustion Reactions
a) Complete Combustion
Definition:
 A chemical reaction in which fuel burns in oxygen
 Common fuels are hydrocarbons with the general
formula CxHy. Methane is CH4, propane is C3H8
 Releases energy in the form of heat and light
5. Combustion Reactions
a) Complete Combustion
Formula: CXHy + O2 (g) → H2O (g) + CO2 (g)
 Occurs when there is plenty of oxygen
 Products are energy, water vapour, and carbon
dioxide
 The ideal way to burn a fuel – it produces the cleanest
(least sooty) and hottest flames
 The blue flame on a gas stove is an example of
complete combustion
Example: Burning of natural gas, CH4
5. Combustion Reactions
b) Incomplete Combustion
Formula: CXHy + O2 (g) → H2O (g) + CO2 (g) + CO (g) + C (s)
 Occurs when the oxygen supply is limited
 Products are energy, water vapour, carbon dioxide,
carbon monoxide, and carbon (soot)
 Flames are often sooty, yellow, and cooler
 The burning of a log in a fireplace is an example of
incomplete combustion
 There are many environmental concerns related to
incomplete combustion
Example: Incomplete combustion of heptane (C8H18), a
hydrocarbon in gasoline
5. Combustion Reactions
Practice:
Compare the complete and incomplete combustion of
propane, C3H8.
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