Learning Goal:
The standard reduction potentials listed in any reference table are only valid at the common reference temperature of 25∘C and standard conditions of 1 MM for solutions and 1 atm for gases. To calculate the cell potential at nonstandard conditions, one uses the Nernst equation,
E=E∘−(2.303RT/nF) log10Q
where E is the potential in volts, E∘ is the standard potential at 25 ∘C in volts, R=8.314J/(K⋅mol) is the gas constant, T is the temperature in kelvins, n is the number of moles of electrons transferred, F=96,500C/(mol e−) is the Faraday constant, and Q is the reaction quotient.
At the common reference temperture of 298 K, substituting each constant into the equation the result is
E=E∘−(0.0592 V/n)log10Q
a) Calculate the standard cell potential at 25 ∘C for
Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s)
b) What is the cell potential for the reaction
Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s)
at 57 ∘C when [Fe2+]= 3.80 MM and [Mg2+]= 0.210 MM .
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