Electron-Transfer Potential
277
set equal to 1. The same will always be done for [H 2 O] and concentrations of
other liquids that appear in half-reaction equations.
We could have combined the equations for E m and £ red into one equation
before solving for£ cell , as follows.
lOg
o ,
0.0591
red
Of particular importance here is the fact that the ratio (Cpox/CGpred is
identical to the ion product for the overall cell reaction, which we shall simply
call Q. In other words, we can write our expression for the voltage of the
whole cell as
ii = £c°eii -
log Q
(17-4)
or the general form of the Nernst equation for the whole cell as
7
£cell = £c°ell -
lOg Q
(17-5)
For the cell reaction
Zn + Cu
2+ +± Zn
2+ + Cu
the corresponding calculation is
77
r^ft^ , ft-7^1 0-0591 ,
[Zn
2+ ]
E ce n = [( + 0.34) - (-0.76)]
^—
log rCu
2+ 1
, ,„
0.0591 ,
101
io4
= +1.01 volts
You should note that Equations 17-4 and 17-5 apply only to chemical equations
that are complete and balanced and that, for a given electron-transfer reaction, n
277
set equal to 1. The same will always be done for [H 2 O] and concentrations of
other liquids that appear in half-reaction equations.
We could have combined the equations for E m and £ red into one equation
before solving for£ cell , as follows.
lOg
o ,
0.0591
red
Of particular importance here is the fact that the ratio (Cpox/CGpred is
identical to the ion product for the overall cell reaction, which we shall simply
call Q. In other words, we can write our expression for the voltage of the
whole cell as
ii = £c°eii -
log Q
(17-4)
or the general form of the Nernst equation for the whole cell as
7
£cell = £c°ell -
lOg Q
(17-5)
For the cell reaction
Zn + Cu
2+ +± Zn
2+ + Cu
the corresponding calculation is
77
r^ft^ , ft-7^1 0-0591 ,
[Zn
2+ ]
E ce n = [( + 0.34) - (-0.76)]
^—
log rCu
2+ 1
, ,„
0.0591 ,
101
io4
= +1.01 volts
You should note that Equations 17-4 and 17-5 apply only to chemical equations
that are complete and balanced and that, for a given electron-transfer reaction, n