Transcript Chemistry 21.2

Chemistry 21.2
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21.2
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.
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21.2
Half-Cells and Cell Potentials > Electrical Potential
Electrical Potential
What causes the electrical potential
of an electrochemical cell?
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21.2
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.
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21.2
Half-Cells and Cell Potentials > Electrical Potential
The difference between the reduction potentials
of the two half-cells is called the cell potential.
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21.2
Half-Cells and Cell Potentials > Electrical Potential
A working voltaic cell can be constructed using a
lemon and strips of copper and zinc.
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21.2
Half-Cells and Cell Potentials > Standard Cell Potential
Standard Cell Potential
What value is assigned to the electrical
potential of a standard hydrogen
electrode?
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21.2
Half-Cells and Cell Potentials > Standard Cell Potential
The standard cell potential (Eocell ) 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.
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21.2
Half-Cells and Cell Potentials > 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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21.2
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.
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21.2
Half-Cells and Cell Potentials > Standard Reduction Potentials
Standard Reduction Potentials
How can you determine the standard
reduction potential of a half-cell?
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21.2
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.
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21.2
Half-Cells and Cell Potentials > Standard Reduction
Potentials
Voltaic Cell
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21.2
Half-Cells and Cell Potentials > Standard Reduction
Potentials
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21.2
Half-Cells and Cell Potentials > Standard Reduction
Potentials
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Half-Cells and Cell Potentials > Standard Reduction
Potentials
Simulation 27
Simulate the operation of voltaic cells.
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21.2
Half-Cells and Cell Potentials > 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?
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21.2
Half-Cells and Cell Potentials > 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.
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21.2
Half-Cells and Cell Potentials > Calculating Standard Cell
Potentials
Table 21.2
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21.2
Half-Cells and Cell Potentials > Calculating Standard Cell
Potentials
Table 21.2
(continued)
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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 21.1
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SAMPLE PROBLEM 21.1
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SAMPLE PROBLEM 21.1
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SAMPLE PROBLEM 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 21.2
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SAMPLE PROBLEM 21.2
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SAMPLE PROBLEM 21.2
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SAMPLE PROBLEM 21.2
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21.2 Section Quiz.
Assess students’ understanding
of the concepts in Section 21.2.
Continue to:
-or-
Launch:
Section Quiz
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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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