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Nernst Equation


Electrochemistry : 10.2 Nernst Equation

NERNST EQUATION 
  • Cell potential (E°cell) under any condition
                  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 
         
  • Ecell = O                           
  • The system reach equilibrium.
  • No more energy release.
  • Cell can do no more work.

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We are group from H5 T34.We create this blog for those who want to learn more about electrochemistry.This is our assigment given by Madam Fazleen .Hopefully all the visitors learn something after opened this blog. ~created by: Zila, Wani, As, Thirah, and Su
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