chemistry 21.1

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Chemistry 21.1

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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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>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?

21.1

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Electrochemical Cells >

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Electrochemical Processes

For any two metals in an activity series, the more active metal is the more readily oxidized.

21.1

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>Electrochemical Cells Electrochemical Processes

A Spontaneous Redox Reaction

21.1

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>Electrochemical Cells Electrochemical Processes21.1

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>Electrochemical Cells Electrochemical Processes21.1

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>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.

21.1

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Electrochemical Cells >

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Voltaic Cells

Voltaic Cells

How does a voltaic cell produce electrical energy?

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>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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>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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>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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>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.

21.1

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>Electrochemical Cells Voltaic Cells

How a Voltaic Cell Works

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21.1 Voltaic Cells>Electrochemical Cells

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21.1 Voltaic Cells>Electrochemical Cells

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Voltaic Cells>Electrochemical Cells21.1

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Voltaic Cells>Electrochemical Cells21.1

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Voltaic Cells>Electrochemical Cells21.1

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>Electrochemical Cells Voltaic Cells

Representing Electrochemical Cells

You can represent the zinc-copper voltaic cell using the following shorthand.

21.1

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Electrochemical Cells >

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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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Electrochemical Cells >

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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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>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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>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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>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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>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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>Electrochemical Cells Using Voltaic Cells as Energy Sources

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>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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>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.

21.1

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Section Quiz

-or-Continue to: Launch:

Assess students’ understanding of the concepts in Section

21.1 Section Quiz.

21.1.

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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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