± The Nernst Equation 17 of 28 Constants | Periodic Table The Nernst equation is
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Question
± The Nernst Equation
17 of 28
Constants | Periodic Table
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??2.303RTnFlog10Q
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 Q is the reaction quotient. At standard temperature, 25 ?C or 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.
Part A
For the reaction
2Co3+(aq)+2Cl?(aq)?2Co2+(aq)+Cl2(g).
E?= ?
what is the cell potential at 25 ?C if the concentrations are [Co3+]= 0.780 M , [Co2+]= 0.656 M , [Cl?]= 0.581 M , and [Cl2]= 0.300 M ?
Express your answer with the appropriate units.
View Available Hint(s)
E =?
Explanation / Answer
2Cl^- (aq) ---------------------> Cl2(g) +2e^- E0 = -1.36v
2Co^3+ (aq) + 2e^- -----------> 2Co^2+ (aq) E0 = 1.82v
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2Cl^- (aq) + 2Co^3+ (aq) ----------> Cl2(g) + 2Co^2+ (aq) E0 cell = 0.46v
n =2
Ecell = E0cell-0.0592/n logQ
= 0.46 - 0.0592/2 log[Co^2+]^2[Cl2]/[Cl^-]^2[Co^3+]^2
= 0.46 - 0.0296 log(0.656)^2*0.3/(0.581)^2*(0.78)^2
= 0.46 -0.0296 log0.6286
= 0.46-0.0296*-0.2016
= 0.466v
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