Nernst Equation The Nernst Equation is a method of calculating cell potential by

Question

Nernst Equation The Nernst Equation is a method of calculating cell potential by using the standard cell potential (E° cell), gas constant (8.315 J/mol K), temperature in Kelvin (T), number of moles of electrons transferred during the reaction (n), Faraday’s constant (F = 96485.335 C/mol), and the reaction quotient (Q).

The equation is as follows: Ecell = E° cell – (RT/nF)*ln(Q)

1. Calculate the cell potential of a galvanic cell made of lead and cadmium. The molarity of the cadmium solution was 0.200 M, and the molarity of the lead solution was 0.100 M. The temperature of the cell is 300 K.

Cd Cd2+ + 2e- E° = +0.403 V

Pb2+ + 2e- Pb E° = -0.126 V

E° cell = _____________________

2. Calculate E° cell of a cell made of zinc and copper. The molarity of the copper solution is 0.300 M, the molarity of the zinc solution is 0.150 M, Ecell is 1.48 V, and the temperature of the cell is 325 K.

Explanation / Answer

Cd Cd2+ + 2e- E° = +0.403 V

Pb2+ + 2e- Pb E° = -0.126 V

-------------------------------------------------------

Cd(s) + Pb^2+(aq) -----------> Cd^2+ (aq) + Pb(s) E0    = 0.277v

     n = 2

Ecell = E° cell – (RT/nF)*ln(Q)

          = 0.277 - 8.314*300/2*96485.335 lnQ

          = 0.277-0.0129ln[Cd^2+]/[pb^2+]

          = 0.277-0.0129 ln0.2/0.1

           = 0.277-0.0129*0.6931   = 0.268v

2.

   Zn(s) ----------> Zn^2+ (aq) + 2e^-

Cu^2+ (aq) + 2e^- ----------> Cu(s)

---------------------------------------------------

Zn(s) + Cu^2+ (aq) -----------> Zn^2+ (aq) + Cu(s)

n =2

Ecell = E° cell – (RT/nF)*ln(Q)

E cell = 1.48v

1.48 = E0 cell -8.314*325/2*96485.335 ln[Zn^2+]/[Cu^2+]

1.48    = E0 cell -0.014ln0.15/0.3

1.48 = E0cell - 0.014*-0.6931

1.48 = E0cell +0.0097

E0 cell = 1.48-0.0097   = 1.47v >>>answer

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