Electrochemistry
Electrochemistry : 10.2 Nernst Equation
 
NERNST  EQUATION - Cell potential (E°cell) under any condition
 
                  E
cell = E
°cell – (
RT/nF) ln Q
R: universal gas constant.            Q : reaction quontient.
N: no. of e- transferred in             T  : absolute temperature (X)
     balanced redox reaction.
F : charge  of 1 mol of e"96.500 C/ mol e-
Example:
 Cd (s) + 2Ag+ (aq) ------ Cd2+(aq) + 2Ag (s)
    Q=[Cd2+]/[Ag+]2 
 Ecell At 25°C (298K)
     Ecell =  E°cell - (
RT/nF) ln Q         (convert to logarithm)
    Ecell = E°cell - (
0.0592/N) log Q  
                      
EFFECT OF CONC . ON CELL POTENTIAL.
  
 Ecell = E°cell - (RT/nF) ln Q             
EXAMPLE 1: 
 Zn (S) +Cu2+ (aq) ------ Zn2+ (aq) + Cu (s)
    Q=[Cd
2+]/[Ag
+]
2 
WHEN Q < 1 = [reactant] > [product]
                       = in Q < 0 , so Ecell > E°cell
WHEN Q > 1 = [reactant] = [product]
                       = in Q = 0 , so Ecell =  E°cell
WHEN Q > 1 = [reactant] < [product]
                       = in Q > 0 , so Ecell < E°cell
 WHEN Q = Kc
    Ecell = E°cell - (0.0592/N) log Q           
- Ecell = O                           
 - The system reach equilibrium.
 - No more energy release.
 - Cell can do no more wore.
 
 
  
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Electrochemistry