The Nernst equation is the one of the most important equations in electrochemist

Question

The Nernst equation is the one of the most important equations in electrochemistry. At standard temperature, 25 ?C or 298 K, the equation has the form

E=E??(0.0591n)logQ

where E? is the standard reduction potential for the reaction in volts and Q is the reaction quotient. 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.

For the reaction 2Co3+(aq)+2Cl(aq) ---> 2Co2+(aq)+Cl2(g). E=0.71 V what is the cell potential at 25 C if the concentrations are [Co3+]= 0.338M , [Co2+]= 0.311M , and [Cl-]= 0.507M and the pressure of Cl2 is PCl2= 9.20atm ?

Express your answer with the appropriate units.

Explanation / Answer

Cell reaction is:

2 Co3+(aq) + 2 Cl-(aq) => 2 Co2+(aq) + Cl2(g)

Eo(cell) = 0.71 V

Moles of electrons transferred n = 2

Nernst equation:

E(cell) = Eo(cell) - (0.0591/n) x log([Co2+]^2.P(Cl2)/([Co3+]^2.[Cl-]^2)

= 0.71 - 0.0591/2 x log(0.311^2 x 9.20/(0.338^2 x 0.507^2))

= 0.666 V (approximately 0.67 V)

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