Chemistry Reference
In-Depth Information
Solution
Zn
2
2 e
£ Zn
(a)
ε
°
0.76 V
(From the table)
(Reversing that
equation and
changing the sign)
(From the table)
(Adding the last two
equations and
their potentials)
Zn £ Zn
2
2 e
ε
°
0.76 V
Cu
2
2 e
£ Cu
ε
°
0.34 V
Cu
2
£ Zn
2
Zn
Cu
ε
°
1.10 V
Ag
e
£ Ag
(b)
ε
°
0.80 V
(From the table)
(
Note:
No change)
(Reversing the
equation from
part a)
(Adding the last two
equations and
their potentials)
2 Ag
2 e
£ 2 Ag
ε
°
0.80 V
Cu £ Cu
2
2 e
ε
°
0.34 V
2 Ag
£ Cu
2
Cu
2 Ag
ε
°
0.46 V
Note that any reactant (or set of reactants) on the left side of an equation
in Table 17.2 will react spontaneously with any product (or set of products) on
the right side of an equation
below
it in the table. When the lower equation is
reversed to make an oxidation half-reaction, and the sign of its potential is
changed, the sum of the two potentials will be positive. For example,
Fe
3
will
Fe
2
Ni
2
,
react with Ni to produce
and
with a standard potential of
0.77 V
(
0.25 V)
1.02 V:
Fe
3
e
£ Fe
2
ε
°
0.77 V
Ni
2
2 e
£ Ni
ε
°
0.25 V
The
reactants
near the top of the table are very powerful oxidizing agents,
and the
products
near the bottom of the table are powerful reducing agents.
Snapshot Review
❒
Standard potentials may be used to determine the tendencies of redox
reactions to proceed.
Sn
4
/Sn
2
ChemSkill Builder 22.1,
22.2
A. Calculate the standard potential of the cell comprised of
and
Pb
2
/Pb.
17.3
The Nernst Equation
A standard cell (Section 17.2) has all solid and liquid reagents pure, all solutes
1.000 M, and all gases at 1.000 atm. However, in practice it is unlikely that
we will want to get these conditions every time we determine a potential. To
