Untitled - Kelly Walsh High School

270 CHEMISTRY FOR THE UTTERLY CONFUSED
If there is an inert electrode present, then show where the inert electrode is with
its phase boundary. If the electrode components are in the same phase, then
separate them by commas; if not, a vertical phase boundary line. For example,
consider the following redox reaction:
Ag (aq) Fe 2 (aq) l Fe 3 (aq) Ag(s)
The oxidation of the ferrous ion to ferric doesn’t involve a solid, so we must use
an inert electrode, such as platinum. The cell notation would then be:
Pt(s) | Fe 2 (aq), Fe 3 (aq) || Ag (aq) | Ag(s)
18-3 Standard Reduction Potentials (E)
In the discussion of the Daniell cell, we indicated that this cell produces a
voltage of 1.10 V. This voltage is really the difference in potential between
the two half-cells. The cell potential (really the half-cell potentials) is
dependent upon concentration and temperature, but initially we’ll simply
look at the half-cell potentials at the standard state of 298 K (25C) and all
components in their standard states (1M concentration of all solutions, 1
atm pressure for any gases and pure solid electrodes). Half-cell potentials
appear in tables as the reduction potentials, that is, the potentials associated
with the reduction reaction. We define the hydrogen half-reaction
(2H (aq) 2e l H 2(g)) as the standard and has been given a value of
exactly 0.00 V. We measure all the other half-reactions relative to it; some
are positive and some are negative. Find the table of standard reduction
potentials in your textbook.
Quick Tip
Here are some things to be aware of in looking at this table:
• All reactions appear in terms of the reduction reaction relative to the standard
hydrogen electrode.
• The more positive the value of the voltage associated with the half-reaction
(E) the more readily the reaction occurs.
• The strength of the oxidizing agent increases as the value becomes more positive,
and the strength of the reducing agent increases as the value becomes more
negative.