ii onor (1etn
(‘hapter I iktrociwinistry
CHAPTER 21
ELECTROCHEMISTRY
PRACTICE PACKET
E LECTROCH EM ICAL CE LIS
Section Review
Objectives
more easily oxidized
• Use the activity series to identify which metal in a pair is
• Identify the source of electrical energy in a voltaic cell
ses to produce
• Describe current technologies that use electrochemical proces
electrical energy
Part A Completion
the concepts and terms
Use this completion exercise to check your understanding of
with a term, short
eted
compl
be
can
that are introduced in this section. Each blank
phrase, or number
1.
Chemical processes can release or absorb energy Any
conversion between chemical energy and electrical is known
1
.
as an
3.
These processes always involve spontaneous redox
reactions in which a transfer of
2
occurs. Electrochemical
cells that generate electrical energy are known as
3
4
.
a
This barrier prevents the contents of the
two half-cells from mixing, but permits the passage of
4.
5.
.
The half-cells of an electrochemical cell are separated by
porous plate or
2.
6.
7.
5
external
between the half-cells. Electrons are transferred through an
circuit from the
the
7
,
6
,
the electrode where oxidation occurs, to
the electrode where reduction occurs.
Answer the following in the space provided.
.
Describe the voltaic cell represented as
) II PbSO(aq) I Pb(s)
aqO
Mg(s) I 4
MgS
(
Sketch a diagram of the cell similar to the one shown in Figure 21.3 of
your textbook. Label the cathode and anode, and indicate the direction
of electron flow.
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DCELL POTENTIALS•
Section Review
Objectives
• Identify the origin of the electrical potential of a cell
• Explain the value of the standard reduction potential of the hydrogen half-cell
• Describe how the standard reduction potential of a half-cell is determined
• Interpret the meaning of a positive standard cell potential
Key Equation
cell
red
oxid
Part A Completion
Use this completion exercise to check your unde
rstanding of the concepts and terms
that are introduced in this section. Each blan
k can be completed with a term, short
phrase, or number.
The measure of a voltaic cell’s ability to produce
current is called its
1
,hi
an electric
1.
is usually measured in volts. The 2.
electrical potential of a cell results from a com
petition for
2
3.
between the two half-cells. The difference betw
een
the reduction
4.
potentials of the two ha1f-rlls is called the
.
5.
3
In comparing standard cell potentials for halfreactions, the
4
serves as a reference and is assigned a valu
e of
5
A negative value for the standard reduction pote
ntial means that
the tendency for this half-cell to be reduced
is
6
than the
tendency for hydrogen ions to be reduced.
If the
calculated
standard cell potential for a given redox react
ion
is positive, then
the reaction is
7
.
6.
7.
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GUIDED PRACTICE PROBLEM 8 (page 676)
F
8. A voltaic cell is constructed using the following half-reactions.
E2+ = +0.34 V
> Cu(s)
(aq) + 2e
2
Cu
Al(s)
AP(aq) + 3e
=
—L66V
Determine the cell reaction and calculate the standard cell potential.
p
Analyze
Step 1. What are the known values?
Step 2. Which half-reaction is a reduction? An oxidation?
ft:
odW4 &i.Lcb.O’y1
Reduction:
C31Nb1 ( th
Oxidation:
Cith’
Step 3. Write both half-reactions in the direction they actually occur.
UY\i
Step 4. What is the expression for the standard cell potential?
(1t
(‘UI
(jJ&ti
UJ’l
I(\hoJ (iu’id.
—
cefl
—
COtv
Calculate
Step 5. Write the cell reaction by adding the half-reactions, making certain that
the number of electrons lost equals the number of electrons gained. The
electrons gained and lost will cancel out.
aq)
[Cu
(
2
+
2e
LiA1(s)
>
Cu(s)]
Al(aq)
+
3e1
step 6. Calculate the standard cell potentiaL
12O
ceII
—
—
Answer thefollowing in the space provided.
<1.
Compute the standard cell potential of a Mg J Mg
2 f Cl
2 C1 cell, using
standard electrode potentials.
©
Ww ftdLuy
flu o’u ut
UWQt1 pctiJvth3J J
uau
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ELECTROLYTIC CELLS
Section Review
Objectives
• Distinguish between
electrolytic and voltaic cells
• Describe the process of electrolysis of water
• Describe the process of electrolysis of brine
• Explain how electrolysis is used in metal processing
Vocabulary
• electrolysis
• electrolytic cell
Part A Completion
Use this completion exercise to check your understanding of the concepts and terms
that are introduced in this section. Each blank can be completed with a term, short
phrase, or number.
The process in which electrical energy is used to make a
nonspontaneous redox reaction go forward is called
1
apparatus in which this process is carried out is called an
In this type of cell, as in voltaic cells,
3
1
The
2
2
.
flow from the anode
4.
to the cathode through an external circuit. In an electrolytic cell,
electrons are driven by an outside power source such as a
In the electrolysis of water, a small amount of
5
4
3.
5.
.
6.
must
7.
be added to enable the water to conduct electricity The products
8.
of the electrolysis of water are
6
and
7
.
During the
electrolysis of brine, chloride ions are oxidized to produce chlorine
gas at the anode, and water is reduced to produce
(-i)
8
at the cathode.
Honor Chem
Chapter 21 Electrochemistry
Compare and Contrast a Voltaic Cell and an Electrolytic Cell
Electrolytic Cell
electrolytic cell.
In the Venn diagram below, write similar and different features of a Voltaic cell and an
Voltaic Cell
S