Electrochemistry : 10.2 Nernst Equation
Electrochemistry

Electrochemistry : 10.2 Nernst Equation



NERNST EQUATION 
                  Ecell = 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=[Cd2+]/[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
        






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