Chemistry 21.1
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21.1
Electrochemical Cells
Fireflies, anglerfish, luminous
shrimp, squid, jellyfish, and even
bacteria give off energy in the
form of light as a result of redox
reactions. You will discover that
the transfer of electrons in a
redox reaction produces energy.
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21.1
Electrochemical Cells
> Electrochemical Processes
Electrochemical Processes
For any two metals in an activity series,
which metal is more readily oxidized?
What type of chemical reaction is
involved in all electrochemical
processes?
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21.1
Electrochemical Cells
> Electrochemical Processes
For any two metals in an activity
series, the more active metal is the
more readily oxidized.
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21.1
Electrochemical Cells
> Electrochemical Processes
A Spontaneous Redox Reaction
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21.1
Electrochemical Cells
> Electrochemical Processes
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21.1
Electrochemical Cells
> Electrochemical Processes
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21.1
Electrochemical Cells
> Electrochemical Processes
Redox Reactions and Electrochemistry
All electrochemical processes involve
redox reactions.
• An electrochemical process is any
conversion between chemical energy and
electrical energy.
• An electrochemical cell is any device
that converts chemical energy into
electrical energy or electrical energy into
chemical energy.
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21.1
Electrochemical Cells
> Voltaic Cells
Voltaic Cells
How does a voltaic cell produce
electrical energy?
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21.1
Electrochemical Cells
> Voltaic Cells
Electrical energy is produced in a voltaic
cell by spontaneous redox reactions
within the cell.
Voltaic cells (named after their inventor)
are electrochemical cells used to convert
chemical energy into electrical energy.
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21.1
Electrochemical Cells
> Voltaic Cells
Constructing a Voltaic Cell
• A half-cell is one part of a voltaic cell in which
either oxidation or reduction occurs.
• The half-cells are connected by a salt
bridge—a tube containing a strong
electrolyte, often potassium sulfate (K2SO4).
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21.1
Electrochemical Cells
> Voltaic Cells
An electrode is a conductor in a circuit that
carries electrons to or from a substance other
than a metal.
• The electrode at which oxidation occurs is
called the anode.
• The electrode at which reduction occurs is
called the cathode.
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21.1
Electrochemical Cells
> Voltaic Cells
Volta built his
electrochemical cell using
piles of silver and zinc
plates separated by
cardboard soaked in salt
water. He used his cell to
obtain an electrical
current.
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21.1
Electrochemical Cells
> Voltaic Cells
How a Voltaic Cell Works
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21.1
Electrochemical Cells
> Voltaic Cells
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21.1
Electrochemical Cells
> Voltaic Cells
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21.1
Electrochemical Cells
> Voltaic Cells
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21.1
Electrochemical Cells
> Voltaic Cells
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21.1
Electrochemical Cells
> Voltaic Cells
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21.1
Electrochemical Cells
> Voltaic Cells
Representing Electrochemical Cells
You can represent the zinc-copper voltaic cell
using the following shorthand.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
Using Voltaic Cells as Energy Sources
What current technologies use
electrochemical processes to produce
electrical energy?
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
Current technologies that use
electrochemical processes to produce
electrical energy include dry cells, lead
storage batteries, and fuel cells.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
Dry Cells
A dry cell is a voltaic cell in which the electrolyte
is a paste. The half reactions for one type of dry
cell are shown below.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
Both dry cells and alkaline batteries are single
electrochemical cells that produce about 1.5 V.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
Lead Storage Batteries
A battery is a group of cells connected together.
The half-reactions for a lead storage battery are
as follows.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
A 12-V car battery consists
of six voltaic cells
connected together. One
cell of a 12-V lead storage
battery is illustrated here.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
Fuel Cells
Fuel cells are voltaic cells in which a fuel
substance undergoes oxidation and from which
electrical energy is continuously obtained.
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21.1
Electrochemical Cells
> Using Voltaic Cells as Energy
Sources
The hydrogen-oxygen fuel cell is a clean source
of power. Such cells are often used in spacecraft.
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21.1 Section Quiz.
Assess students’ understanding
of the concepts in Section 21.1.
Continue to:
-or-
Launch:
Section Quiz
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21.1 Section Quiz.
1. Zn is above Pb in the activity series of metals.
Which of the following statements is correct?
a. Zn will react with Pb2+.
b. Pb2+ will react with Zn2+.
c. Zn2+ will react with Pb.
d. Pb will react with Zn2+.
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21.1 Section Quiz.
2. The reactions that take place in
electrochemical cells involve electron
transfers. What name is given to such
reactions?
a. oxidation reactions
b. reduction reactions
c. spontaneous redox reactions
d. double replacement reactions
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21.1 Section Quiz.
3. Portable sources of electrical energy
consisting of groups of voltaic cells connected
together are called
a. batteries
b. alkaline cells.
c. dry cells.
d. fuel cells.
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21.1 Section Quiz.
4. In an automobile storage battery, sulfuric acid
(H2SO4) is used as the
a. cathode.
b. electrolyte.
c. anode.
d. oxidizing agent.
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21.1 Section Quiz.
5. In the hydrogen-oxygen fuel cell, the
product(s) of the overall reaction is/are
a. water and hydroxide ions.
b. hydrogen and oxygen.
c. water.
d. hydroxide ions.
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