The Nemst equation is one of the most important equations in electrochemistry. T

Question

The Nemst equation is one of the most important equations in electrochemistry. To calculate the cell potential at non-standard-state conditions, the equation is E = E degree - 2.303 RT/nF log_10 Q where E is the potential in volts, E degree 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 Q is the reaction quotient. At standard temperature. 25 degree C or 298 K. the equation has the form E = E degree - (0.0592/n) log Q The reaction quotient has the usual form Q = [products]^x/[reactants]^y 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 Nemst equation allows for the calculation of the cell potential E at other conditions of concentration and pressure. For the reaction 2Co^3+ (aq) + 2Cl^- (aq) rightarrow 2Co^2+ (aq) + Cl_2 (g). E degree = 0.483 V what is the cell potential at 25 degree C if the concentrations are [Co^3+] = 0.113 M, [Co^2+] = 0.226 M, and [Cl^-] = 0.494 M and the pressure of Cl_2 is P_cl2 = 4.30 atm? Express your answer with the appropriate units.

Explanation / Answer

Eo cell = Eo ( Co3+/Co2+) - Eo( Cl2/2Cl-) = 1.81 - 1.36 =0.45

K of cell = pCl2 x [Co2+]^2 / [Co3+]^2 [Cl-]^2 = 4.3 x 0.226^2 / ( 0.113^2 x 0.494^2) = 70.48

Ecell = Eo cell - ( 0.059/n) log K   where n = number of electrons involved per reaction = 2 ( 2Cl- reduced to Cl2 takes 2e-)

now E cell = 0.45 - (0.059/2) log ( 70.48)

=0.396 volts

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