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206 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 20
The two parts of a voltaic cell are called half-cells. Each halfcell contains an electrode, which conducts electrons into or out of
the half-cell. The electrode where oxidation occurs is called the
anode, and the electrode where reduction occurs is called the
cathode. In the previous example, the nickel strip is the anode and
the copper strip is the cathode.
Calculating cell potential The tendency of a substance to gain
electrons is called its reduction potential. The reduction potential
of a half-cell reaction is expressed in volts (V). Chemists measure
the reduction potentials of half-cells against the standard hydrogen
electrode, which has a reduction potential defined as 0 V at 25°C,
1.0 atm pressure, and 1M hydrogen ion concentration.
Table 20-1 on page 712 of your textbook lists the standard
reduction potentials (E 0 values) of common half-cell reactions.
These values apply to the standard conditions of a 1M solution,
25°C, and 1 atm pressure. In any voltaic cell, the half-reaction with
the lower reduction potential will proceed in the opposite direction,
as an oxidation half-reaction. The half-reaction with the higher
reduction potential will proceed as a reduction. The electrical potential of a voltaic cell, also called the cell potential, is found by
subtracting the standard reduction potential of the oxidation halfreaction from the standard reduction potential of the reduction
half-reaction.
E 0
cell ϭ E 0
reduction Ϫ E 0
oxidation
For example, suppose the redox reaction considered previously is
carried out in a voltaic cell under standard conditions. The E 0 values
of the half-reactions can be found in Table 21-1 in your textbook.
Ni 2ϩ (aq) ϩ 2e Ϫ 0 Ni(s) E 0 ϭ Ϫ0.257 V
Cu 2ϩ (aq) ϩ 2e Ϫ 0 Cu(s) E 0 ϭ ϩ0.3419 V
The first half-reaction has the lower reduction potential, so it proceeds as an oxidation. As expected, the half-reactions of the overall
redox reaction are as follows.
Ni(s) 0 Ni 2ϩ (aq) ϩ 2e Ϫ (oxidation)
Cu 2ϩ (aq) ϩ 2e Ϫ 0 Cu(s) (reduction)
▲
206 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 20
The two parts of a voltaic cell are called half-cells. Each halfcell contains an electrode, which conducts electrons into or out of
the half-cell. The electrode where oxidation occurs is called the
anode, and the electrode where reduction occurs is called the
cathode. In the previous example, the nickel strip is the anode and
the copper strip is the cathode.
Calculating cell potential The tendency of a substance to gain
electrons is called its reduction potential. The reduction potential
of a half-cell reaction is expressed in volts (V). Chemists measure
the reduction potentials of half-cells against the standard hydrogen
electrode, which has a reduction potential defined as 0 V at 25°C,
1.0 atm pressure, and 1M hydrogen ion concentration.
Table 20-1 on page 712 of your textbook lists the standard
reduction potentials (E 0 values) of common half-cell reactions.
These values apply to the standard conditions of a 1M solution,
25°C, and 1 atm pressure. In any voltaic cell, the half-reaction with
the lower reduction potential will proceed in the opposite direction,
as an oxidation half-reaction. The half-reaction with the higher
reduction potential will proceed as a reduction. The electrical potential of a voltaic cell, also called the cell potential, is found by
subtracting the standard reduction potential of the oxidation halfreaction from the standard reduction potential of the reduction
half-reaction.
E 0
cell ϭ E 0
reduction Ϫ E 0
oxidation
For example, suppose the redox reaction considered previously is
carried out in a voltaic cell under standard conditions. The E 0 values
of the half-reactions can be found in Table 21-1 in your textbook.
Ni 2ϩ (aq) ϩ 2e Ϫ 0 Ni(s) E 0 ϭ Ϫ0.257 V
Cu 2ϩ (aq) ϩ 2e Ϫ 0 Cu(s) E 0 ϭ ϩ0.3419 V
The first half-reaction has the lower reduction potential, so it proceeds as an oxidation. As expected, the half-reactions of the overall
redox reaction are as follows.
Ni(s) 0 Ni 2ϩ (aq) ϩ 2e Ϫ (oxidation)
Cu 2ϩ (aq) ϩ 2e Ϫ 0 Cu(s) (reduction)
▲