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Monday, January 24, 2011

Faraday law

FARADAY LAW
  • Amount of substance produce of each electrode is directly proportional to quantity of charge flowing through the cell
  • Also called Faraday's First Law of electrolysis.

CALCULATING USING FARADAY'S LAW
  • Main steps
    • Balance half reaction to find number of moles of electrons.
    • Needed per mole product.
    • Use Faraday's constant (96500C / mol ) to find corresponding charge.
    • Use molar mass / mole to find charge needed for a given mass / mole of product

ELECTRIC CHARGE (Q)

Charge ( Q )         =    Current ( I )    ×    time ( t )
Unit Coulomb , C        Ampere , A        Second , s







10.2 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.

Sunday, January 23, 2011

Standard hydrogen potential

Standard Reduction Potentials
Standard reduction potential (E0) is the voltage associated with a reduction reaction at an electrode when all solutes are 1 M and all gases are at 1 atm.

Standard hydrogen electrode (SHE)
 
Reduction Reaction
                                       

             E0 = 0 V

 

Galvanic cell

                           Oxidation
is defined as
  • the addition of oxygen to a substance
  • the loss of hydrogen from a substance
  • the process of electron loss from a substance
  • an increase in the oxidation number of a substance

                         Reduction

is define as
  • the loss of oxygen from a substance
  • the addition of hydrogen to a substance
  • the process of electron gain in a substance
  • a decrease in oxidation number of a substance
                     Redox reaction


are reaction involving oxidation and reduction

Thursday, January 20, 2011

Electrochemical

Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

Electrochemical
Electrochemical processes are oxidation-reduction reactions in which:
the energy released by a spontaneous reaction is converted to electricity or
electrical energy is used to cause a nonspontaneous reaction to occur
  
Oxidation half-reaction (lose e-)
 
          Reduction half-reaction (gain e-)


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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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