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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 COSF6 Na2S2O3
NO3- HAsO2
KMnO4 XeOF4
P4O6Na2C2O4
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 + 2Agb) 4KClO3(s) KCl(s) + 3KClO4(s)c) 3AgNO3(aq) + K3PO4(aq) Ag3PO4(s) + 3KNO3(aq)