General Information: The Nernst equation is one of the most important equations

Question

General Information: The Nernst equation is one of the most important equations in electrochemistry. To calculate the cell potential at non-standard-state conditions, the equation is

E=E2.303RTnFlog10Q

where E is the potential in volts, E is the standard potential in volts, R is the gas constant, T is the temperature in kelvins, n is the number of moles of electrons transferred, F is the Faraday constant, and Qis the reaction quotient. At standard temperature, 25 Cor 298 K, the equation has the form

E=E(0.0592n)logQ

The reaction quotient has the usual form

Q=[products]x[reactants]y

A table of standard reduction potentials gives the voltage at standard conditions, 1.00 M for all solutions and 1.00 atm for all gases. The Nernst equation allows for the calculation of the cell potential E at other conditions of concentration and pressure.

Question:

For the reaction

2Co3+(aq)+2Cl(aq)2Co2+(aq)+Cl2(g).  E=0.483 V

what is the cell potential at 25 C if the concentrations are [Co3+]= 0.287 M , [Co2+]= 0.262 M , and [Cl]= 0.815 M and the pressure of Cl2 is PCl2= 6.10 atm ?

Explanation / Answer

2Cl- -2e--->Cl2

2Co3+ +2e--->2Co2+

E=E(0.0592/n)logQ n=2mol electron exchanged by reducing as well as oxidizing agent

   =0.483 - (0.0592)/2 log [Co2+]^2 *pcl2/[Co3+]^2 [Cl-]^2

    =0.483V-0.0296 V log (0.262)^2 *(6.10atm) /(0.287)^2 (0.815)^2

     =0.483-0.0296 log 7.653

     =0.483-0.0296 *0.884

     =0.457 V

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