Types of Reactions
Types of Reactions
•
•
•
•
•
•
Synthesis (Combination)
Decomposition
Single Displacement
Double Displacement
Combustion
Oxidation-Reduction (Redox)
Synthesis
• In a synthesis reaction, two
substances react to form one
new substance.
• A + B  AB
• A and B can be either an
element or a compound
• 2 Na + Cl2  2 NaCl
• CaO + CO2  CaCO3
Decomposition
• In a decomposition reaction,
one compound breaks down into
two or more simple substances.
• AB  A + B
• 2 HgO  2 Hg + O2
• 2 KClO3  2 KCl + 3 O2
Single Displacement
• In a single displacement reaction, an
uncombined element replaces
another element in a compound.
• Metals replace metals and
nonmetals replace nonmetals.
• The uncombined element must be
more chemically reactive than the
element it is replacing in order for
the reaction to occur.
• A + BC  B + AC
Examples of Single
Displacement Reactions
• Zn + CuSO4  Cu + ZnSO4
• Cl2 + 2 NaBr  2 NaCl + Br2
• Na + H2O  NaOH + H2
Double Displacement
• In a double displacement
reaction, the positive and
negative ions “change partners”
and form two new compounds.
• Three types of products may
result: a weak/nonelectrolyte, a
precipitate, or a gas.
• AB + CD  AD + CB
Formation of a
Weak/Nonelectrolyte
• HCl + NaOH  NaCl + H2O
• The above reaction is also
referred to as a neutralization
reaction.
• Neutralization reactions involve
the reaction of an acid and base
to produce a salt and water.
Formation of a
Precipitate
• AgNO3 + NaCl  AgCl + NaNO3
• The AgCl is an insoluble salt and will
precipitate out of the solution.
Formation of a Gas
• 2HCl + CaCO3  CaCl2 + H2CO3
• The H2CO3 decomposes to H2O
and CO2.
• 2HCl + CaCO3 CaCl2 + H2O + CO2
Another example
• MnS + 2HCl  MnCl2 + H2S
Combustion
• In a combustion reaction, a
hydrocarbon reacts with oxygen
to produce carbon dioxide and
water.
• CxHy + O2  CO2 + H2O
Oxidation-Reduction
(Redox) Reactions
• Oxidation-reduction reactions
are those that involve the
transfer of one or more
electrons.
• All of the previous types of
reactions except double
displacement are also examples
of redox reactions.
Oxidation States
• Oxidation states (or oxidation
numbers) are a way to keep track of
electrons in redox reactions.
• Oxidation states are obtained in
covalent molecules by arbitrarily
assigning the electrons to particular
atoms.
• Actual charges on ions are written
as n+ or n- while oxidation states (not
actual charges) are written as +n or
-n.
Rules for Assigning
Oxidation States
• The oxidation state of an atom in an
element is 0.
• The oxidation state of a monatomic ion is
the same as its charge.
• In compounds, fluorine is always -1.
• Oxygen is usually -2.
• Hydrogen is +1 if combined with
nonmetals.
• The sum of the oxidation states in a
neutral compound must be zero.
• The sum of the oxidation states in an ion
must equal the charge on the ion.
Assigning Oxidation
States
• Assign the oxidation states to
all atoms in the following (Note:
Check answers on following slide)
CO2
SF6
NO3KMnO4
P4O6
CO
Na2S2O3
HAsO2
XeOF4
Na2C2O4
Answers
•
•
•
•
•
•
•
•
•
•
C=+4, O=-2
S=+6, F=-1
N=+5, O=-2
K=+1, Mn=+7, O=-2
P=+3, O=-2
C=+2, O=-2
Na=+1, S=+2, O=-2
H=+1, As=+3, O=-2
Xe=+6, O=-2, F=-1
Na=+1, C=+3, O=-2
Characteristics of
Oxidation-Reduction
Reactions
• Redox reactions are characterized
by a transfer of electrons
• Oxidation is an increase in oxidation
state or a loss of electrons.
• Reduction is a decrease in oxidation
state or a gain of electrons.
• OIL RIG
• Oxidation is loss; Reduction is gain
Characteristics of
Oxidation-Reduction
Reactions (continued)
• The oxidizing agent is the
electron acceptor and
consequently undergoes
reduction.
• The reducing agent is the
electron donor and
consequently undergoes
oxidation.
Identifying Oxidizing and
Reducing Agents.
•
Identify the oxidizing agent,
reducing agent, the species
oxidized, and the species reduced
for each of the following:
a) 2AgNO3 + Cu  Cu(NO3)2 + 2Ag
b) 4KClO3(s)  KCl(s) + 3KClO4(s)
c)
3AgNO3(aq) + K3PO4(aq)  Ag3PO4(s) + 3KNO3(aq)