Chemistry Reference
In-Depth Information
Li K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb
H
2
Sb Cu Ag Hg Pd Pt Au
E° < 0
E° > 0
Not displace H
2
from H
2
O
(l)
,
steam or acid
Displace H
2
from H
2
O
(l)
, steam or acid
Ease of oxidation increases
FIGURE 3.5
Electrochemical series of metals.
TABLE 3.2
Table of Standard Reduction Potential
Oxidizing Agents
Reducing Agents
E° (V)
Strong
F
2
(g)
+ 2e
−
2F
−
Weak
2.87
→
+ 5e
−
Mn
2+
+ 4H
2
O
1.51
−
+
→
MnO H
4
+
Ag
+
+ e
−
→
Ag
(s)
0.799
Cu
2+
+ 2e
−
→
Cu
(s)
0.337
2H
+
(aq)
+ e
−
→
H
2(g)
0.000
Pb
2+
+ 2e
−
Pb
(s)
−0.126
→
Zn
2+
+ 2e
−
Zn
(s)
−0.763
→
Weak
Li
+
+ e
−
Li
(s)
Strong
−3.05
→
Source:
Adapted from B.G. Segal,
Chemistry
:
Experiments and Theory
(New York:
Wiley, 1989).
By devising various galvanic cells and measuring their electromotive forces, tables
of values of standard electrode potentials can be constructed. A table that lists the
value of electrode potential for any half-cell in which all concentrations are 1M and
all gases are at 1-atm pressure is a Table of Standard Reduction Potential (Table 3.2).
By convention, the tabulated values are standard reduction potentials relative to the
potential of the standard hydrogen electrode, which is defined as exactly zero volts.
The analysis of the data from Table 3.2 highlights some important aspects.
1. Oxidizing agents are tabulated at the left of the table in the decreasing order
of the oxidizing power.
2. The strongest oxidizing agent is fluorine gas, F
2
.
3. The reducing agents are written at the right of the table in the increasing
order of the reducing power.
4. The strongest reducing agent is lithium metal.
5. The more positive the reduction potential, the weaker the reducing agent
and conversely, the more negative the reduction potential, the stronger the
reducing agent.
It can be surprising that lithium is the stronger reducing agent, although cesium
is the most electropositive metal. This behavior can be explained if all the processes
are included in the reduction process (
Figure 3.6
)
. The standard reduction potential
is related to the free energy change: ΔG
o
= − nFE
o
, and ΔG
o
= ΔH
o
− TΔS
o
.
