Slide 1 of 38 Chemistry 21.2. © Copyright Pearson Prentice Hall Slide 2 of 38 Half-Cells and Cell...

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Chemistry 21.2

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Half-Cells and Cell Potentials

Batteries provide current to power lights and many kinds of electronic devices—such as the personal digital assistant shown here. You will learn how to calculate electrical potential.

21.2

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Half-Cells and Cell Potentials >

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Electrical Potential

Electrical Potential

What causes the electrical potential of an electrochemical cell?

21.2

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>Half-Cells and Cell Potentials Electrical Potential

The electrical potential of a cell results from a competition for electrons between two half-cells.

• The electrical potential of a voltaic cell is a measure of the cell’s ability to produce an electric current.

• The tendency of a given half-reaction to occur as a reduction is called the reduction potential.

21.2

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>Half-Cells and Cell Potentials Electrical Potential

The difference between the reduction potentials of the two half-cells is called the cell potential.

21.2

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>Half-Cells and Cell Potentials Electrical Potential

A working voltaic cell can be constructed using a lemon and strips of copper and zinc.

21.2

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Standard Cell Potential

Standard Cell Potential

What value is assigned to the electrical potential of a standard hydrogen electrode?

21.2

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>Half-Cells and Cell Potentials Standard Cell Potential

The standard cell potential (Eo ) is the measured cell potential when the ion concentrations in the half-cells are 1M, any gases are at a pressure of 101 kPa, and the temperature is 25°C.

21.2

cell

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>Half-Cells and Cell Potentials21.2 Standard Cell Potential

The standard hydrogen electrode is used with other electrodes so the reduction potentials of the other cells can be measured.

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>Half-Cells and Cell Potentials Standard Cell Potential

The standard reduction potential of the hydrogen electrode has been assigned a value of 0.00 V.

21.2

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Half-Cells and Cell Potentials >

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Standard Reduction Potentials

Standard Reduction Potentials

How can you determine the standard reduction potential of a half-cell?

21.2

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>Half-Cells and Cell Potentials Standard Reduction Potentials

You can determine the standard reduction potential of a half-cell by using a standard hydrogen electrode and the equation for standard cell potential.

21.2

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>Half-Cells and Cell Potentials Standard Reduction Potentials

Voltaic Cell

21.2

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>Half-Cells and Cell Potentials Standard Reduction Potentials

21.2

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>Half-Cells and Cell Potentials Standard Reduction Potentials

21.2

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Half-Cells and Cell Potentials >

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Standard Reduction Potentials

Simulation 27

Simulate the operation of voltaic cells.

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Calculating Standard Cell Potentials

Calculating Standard Cell Potentials

How can you interpret the cell potential of a redox reaction in terms of the spontaneity of the reaction?

21.2

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Calculating Standard Cell Potentials

If the cell potential for a given redox reaction is positive, then the reaction is spontaneous as written. If the cell potential is negative, then the reaction is nonspontaneous.

21.2

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>Half-Cells and Cell Potentials Calculating Standard Cell Potentials

21.2

Table 21.2

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>Half-Cells and Cell Potentials Calculating Standard Cell Potentials

Table 21.2

(continued)

21.2

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Determining Reaction Spontaneity

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Determining Reaction Spontaneity

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Determining Reaction Spontaneity

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Practice Problems for Conceptual Problem 21.1

Problem Solving 21.9 Solve Problem 9 with the help of an interactive guided tutorial.

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SAMPLE PROBLEM

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21.1

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SAMPLE PROBLEM

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21.1

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SAMPLE PROBLEM

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21.1

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SAMPLE PROBLEM

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21.1

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Practice Problems for Sample Problem 21.1

Problem Solving 21.12 Solve Problem 12 with the help of an interactive guided tutorial.

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SAMPLE PROBLEM

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21.2

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SAMPLE PROBLEM

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21.2

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SAMPLE PROBLEM

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21.2

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SAMPLE PROBLEM

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21.2

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Section Quiz

-or-Continue to: Launch:

Assess students’ understanding of the concepts in Section

21.2 Section Quiz.

21.2.

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21.2 Section Quiz.

1. The electrical potential of a cell results from the competition for _________ between two half-cells.

a. electrolytes

b. electrons

c. oxygen

d. protons

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21.2 Section Quiz.

2. All half-cell potentials are measured relative to the standard

a. hydrogen electrode.

b. platinum electrode.

c. oxygen electrode.

d. copper electrode.

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21.2 Section Quiz.

3. The standard reduction potential of a half-cell is determined by comparing it to the

a. standard hydrogen electrode.

b. oxidation-half cell.

c. fluorine half-cell.

d. lithium half-cell.

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21.2 Section Quiz

4. Choose the correct words for the spaces. If the cell potential for a given redox reaction is ______, then the reaction is spontaneous as written. If the cell potential is ________, then the reaction is nonspontaneous.

a. negative, positive

b. positive, negative

c. zero, positive

d. negative, zero

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