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Chemistry 2
Chapter 5- Chemical
Reactions and Quantities
5.1 – Chemical Changes
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Physical Change – appearance
altered; no composition change
Chemical Change – new stuff formed
5.2 – Chemical Equations

__Pb(NO3)2(aq) + __NaCl(aq) 
__PbCl2(s) + __NaNO3(aq)
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Reactants? Products?
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Balanced?
• 1:2:1:2
5.3 – Types of Reactions
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Synthesis – many things into one
thing
A + B  AB
5.3 – Types of Reactions
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Decomposition – one thing breaks
into many things
AB  A + B
5.3 – Types of Reactions
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Single-Replacement – one thing
switches with one other thing
• Only a (+) charged ion can replace
another (+) charge…same for (-) ions
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A + BC  AC + B
5.3 – Types of Reactions

Double-Replacement – two things
switch spots
• (+) charges switch with each
other…same for (-) charges
• like “foil-ing” in math…outsides go
together and insides go together
5.4 – Oxidation-Reduction
Reactions
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Oxidation-Reduction – reactions with
a loss and a gain of electrons among
the reactants
“LEO the lion goes GER”
• Loss of electrons is oxidation…gain of
electrons is reduction.
5.4 – Oxidation-Reduction
Reactions
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Ca + S  Ca+2 + S-2 = CaS
Calcium becomes more positive, so it
loses electrons…oxidation.
• Ca  Ca+2 + 2e-
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Sulfur becomes more negative, so it
gains electrons…reduction.
• S + 2e-  S-2
5.4 – Oxidation-Reduction
Reactions
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Zn + CuSO4  ZnSO4 + Cu
Zn + Cu+2 + SO4-2 
Zn+2 + SO4-2 + Cu

Zn  Zn+2 + 2e-
(oxidation)

Cu+2 + 2e-  Cu
(reduction)
5.4 – Oxidation-Reduction
Reactions
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P. 165
#16, 18
5.4 – Oxidation-Reduction
Reactions
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Balancing Redox Reactions
Use the following oxidation number
method.
_HNO3(aq) + _H3AsO3(aq) 
_NO(g) + _H3AsO4(aq) + _H2O(l)
Balancing Redox Reactions

Step 1: Try to balance the atoms in
the equation by inspection, that is,
by the standard technique for
balancing non-redox equations.
(Many equations for redox reactions
can be easily balanced by
inspection.) If you successfully
balance the atoms, go to Step 2. If
you are unable to balance the atoms,
go to Step 3.
Balancing Redox Reactions

Step 2: Check to be sure that the
net charge is the same on both sides
of the equation. If it is, you can
assume that the equation is correctly
balanced. If the charge is not
balanced, go to Step 3.
Balancing Redox Reactions

Step 3: If you have trouble
balancing the atoms and the charge
by inspection, determine the
oxidation numbers for the atoms in
the formula, and use them to decide
whether the reaction is a redox
reaction. If it is not redox, return to
Step 1 and try again. If it is redox,
go to Step 4.
Balancing Redox Reactions

Step 4: Determine the net increase
in oxidation number for the element
that is oxidized and the net decrease
in oxidation number for the element
that is reduced.
Balancing Redox Reactions
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Step 5: Determine a ratio of
oxidized to reduced atoms that
would yield a net increase in
oxidation number equal to the net
decrease in oxidation number (a
ratio that makes the number of
electrons lost equal to the number of
electrons gained).
Balancing Redox Reactions
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Step 6: Add coefficients to the
formulas so as to obtain the correct
ratio of the atoms whose oxidation
numbers are changing. (These
coefficients are usually placed in
front of the formulas on the reactant
side of the arrow.)
Balancing Redox Reactions
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Step 7: Balance the rest of the
equation by inspection.
2:3:2:3:1
Balancing Redox Reactions
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Another example…
_Cu(s) + _HNO3(aq) 
_Cu(NO3)2(aq) + _NO(g) + _H2O(l)
3:8:3:2:4
5.5 – The Mole