Download Synthesis and Decomposition Reactions - SCH3U-CCVI

Types of Chemical
Reactions
Outline
 Types
of Reactions – the 5 types
 Synthesis and Decomposition
Chemical Reactions
 Chemical
reactions can be grouped into
five categories:
 Synthesis/Combination
 Decomposition
 Single
displacement
 Double displacement
 Combustion
Chemical Reactions
 Today
we will focus on synthesis and
decomposition
LEARNING GOAL:
Be able to identify and predict the
products for synthesis and
decomposition reactions
Synthesis Reaction
 Synthesis
Reaction – Two or more
substances (elements or compounds)
react to form ONE product.
Combination of smaller atoms/molecules
into larger molecules.
 Usually exothermic (energy is produced)
 Can occur naturally or by an initial
application of energy (heat, flame, UV
light, use of catalyst)
Synthesis Reaction
A + B  AB
 eg.
2H2 + O2  2H20
2Na (s) + Cl2(g)  2NaCl (s) + energy
Synthesis Reaction
Predicting Products
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Metal + oxygen → metal oxide (basic oxide)
EX. 2Mg(s) + O2(g) → 2MgO(s)
Nonmetal + oxygen → nonmetallic oxide (acidic oxide)
EX. C(s) + O2(g) → CO2(g)
Metal oxide + water → metallic hydroxide (base)
EX. MgO(s) + H2O(l) → Mg(OH)2(s)
Nonmetallic oxide + water → acid
EX. CO2(g) + H2O(l) → ; H2CO3(aq)
Metal + nonmetal → salt
EX. 2 Na(s) + Cl2(g) → 2NaCl(s)
A few nonmetals combine with each other.
EX. 2P(s) + 3Cl2(g) → 2PCl3(g)
These two reactions must be remembered:
N2(g) + 3H2(g) → 2NH3(g)
NH3(g) + H2O(l) → NH4OH(aq)
Decomposition Reaction
 Decomposition
Reaction – ONE reactant
produces two or more products.
Splitting of large molecules into
elements or smaller molecules.
 Usually endothermic (requires energy)
 Can require energy in the form of heat,
electricity, catalyst, UV light
 *some decomposition rxns occur at room
temperature
Decomposition Reaction
AB  A + B
 Eg.
2H20  2H2 + O2
2NaCl (s)  2Na (s) + Cl2(g)
(heat/electricity required)
Decomposition Reaction
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Predicting Products
Metallic carbonates, when heated, form metallic oxides and
CO2(g).
EX. CaCO3(s) → CaO(s) + CO2(g)
Most metallic hydroxides, when heated, decompose into
metallic oxides and water.
EX. Ca(OH)2(s) → CaO(s) + H2O(g)
Metallic chlorates, when heated, decompose into metallic
chlorides and oxygen.
EX. 2KClO3(s) → 2KCl(s) + 3O2(g)
Some acids, when heated, decompose into nonmetallic
oxides and water.
EX. H2SO4 → H2O(l) + SO3(g)
Some oxides, when heated, decompose.
EX. 2HgO(s) → 2Hg(l) + O2(g)
Some decomposition reactions are produced by electricity.
EX. 2H2O(l) → 2H2(g) + O2(g)
EX. 2NaCl(l) → 2Na(s) + Cl2(g)