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.

Using the reaction and the E? given below: 2Co3+(aq)+2Cl?(aq)?2Co2+(aq)+Cl2(g)      E?=0.46 V

what is the cell potential at 25 ?C if the concentrations are [Co3+]= 0.138M , [Co2+]= 0.697M , and [Cl?]= 0.261M and the pressure of Cl2 is PCl2= 7.90atm?

Please help with understanding, thank you!

Explanation / Answer

n the given reaction there is a 2-electron change (i.e. 2Co3+ ==> 2Co2+). Also,

Q = ([Co2+]^2 PCl2) / ([Co3+]^2 [Cl-]^2) = ((0.697)^2 (7.90)) / ((0.138)^2 (0.261)^2) = 2958.3

E cell = Eo cell - 0.059/n log Q = 0.46 - 0.059/2 log (2958.3) = 0.36 V

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