AP Chemistry: Electrochemistry
Equilibrium Constants and E cell and G
What does G represent?
The maximum useful work of a reaction
For a voltaic cell, this is the electrical work and it is negative
G = ­nFE cell
n = moles of electrons transferred
F = Faraday constant
96,485 Coulombs/mole e­
Using E cell, calculate G for this reaction:
Zn + Cu+2 Zn+2 + Cu
G = ­nFE cell
G = ­(2) (96,485) (1.10)
(couloumbs x volts = Joules)
G = ­3.01 x 105 J = ­301 kJ
*of course, now you can calculate cell potential from G values! Hooray!
Relating K, G and E
AP Chemistry: Electrochemistry
Equilibrium Constants and E cell and G
G = ­nFE cell
and
G = ­RT lnK
So...
­nFE cell = ­RT lnK
E cell
­RT lnK
=
­nF
E cell = 0.0592
log K
n
Calculate the equilibrium constant for
the following voltaic cell reaction:
Zn (s) Zn+2 (aq) Cu+2 (aq) Cu (s)
E cell = 0.0592
log K
n
log K =
n E cell
2.20
= (2) (1.10) =
= 37.2
0.0592
0.0592
0.0592
10­37.2 = 1.58 x 1037
Zn + Cu+2 (aq) Zn+2 (aq) + Cu
[Zn+2] K = Kc = [Cu+2] Relating K, G and E
AP Chemistry: Electrochemistry
G
K
E cell
Calorimetry data
G = H ­T S
G
Electrochemical
data
Relating K, G and E
E cell
K
Equilibrium composition
data