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

Question

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 = 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]'/[reactants]' A table of standard reduction potentials gives the voltage at standard conditions, 100 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 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+] = 1 0810 M, [Co^2+] = 0.594 M and [Cl^-] = 0.0719 M and the pressure of Cl_2 is P_Cl_2 = 3.30 atm? Express your answer with the appropriate units.

Explanation / Answer

Given

[Co3+] = 0.81 M [ Co2+] = 0.594 M [Cl-] = 0.719 M pCl2 = 3.3 atm

Eo = 0.483 V

reaction is

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

Q = [Co2+]2 * pCl2 / [Co3+]2 [Cl-]2 = 0.5942 * 3.3 / 0.812 * 0.7192 = 3.433

no. of electrons n = 2

Ecell = Eo cell - ( 0.0592 /n ) log Q = 0.483 V - ( 0.0592/2) log (3.433) = 0.499 V Answer

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