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Class 12th Chemistry Online Class For 100% Result
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Nernst Equation

  • This equation was named after a German physicist Walther Nernst.
Class 12 Electrochemistry Notes
Class 12 Electrochemistry Notes
  • The Nernst Equation empowers the assurance of cell potential under non-standard conditions and relates the measured cell potential to the reaction quotient and permits the exact measurement of equilibrium constants.
  • Let us consider an electrochemical reaction of the following type:

aA +bB  –> cC + dD

  • Nernst equation for this can be written as follows:
  • If the circuit in Daniel cell is closed:

Zn(s) + Cu2+ (aq) →Zn2+ (aq) + Cu(s)

Class 12 Electrochemistry Notes

Problem:

Calculate the emf of the cell in which the following reaction takes place: Ni(s) + 2Ag+ (0.002 M) → Ni2+ (0.160 M) + 2Ag(s). Given that Eøcell = 1.05 V.


Electrochemical Cell and Gibbs Energy of the Reaction

Class 12 Electrochemistry Notes
Class 12 Electrochemistry Notes
  • Electrical work done (1 second) = Electrical potentialX Total charge passed
  • Passing the charges reversibly through the galvanic cell results in maximum work.
  • Reversible work done by galvanic cell = Decrease in Gibbs energy
  • Let E = Emf of the cell

           nF = Amount of charge passed

        Δr= Gibbs energy of the reaction

        ΔrG = -nFEcell

  For the reaction,

           Zn(s) + Cu2+ (aq) –> Zn2+ (aq) + Cu(s)

            [ΔrG = -2FEcell  ]

But when the equation becomes

2Zn(s) + 2Cu2+ (aq) –> 2Zn2+ (aq) + 2Cu(s)

  [ΔrG = -4FEcell  ]

Problem:

The cell in which the following reactions occurs:

Class 12 Electrochemistry Notes

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