To learn how to use the Nernst equation. The standard reduction potentials liste

Question

To learn how to use the Nernst equation. The standard reduction potentials listed in any reference table are only valid at standard-state conditions of 25 degree C and 1 M. To calculate the cell potential at non-standard state conditions, one uses the Nernst equation, E = E degree - 2.303 RT/nF log_10 Q where E is the potential in volts, E is the standard potential in volts, R = 8.314 J/(K middot mol) is the gas constant, T is the temperature in kelvins, n is the number of moles of electrons transferred, F = 96,500 C/(mol e^-) is the Faraday constant, and Q is the reaction quotient. Substituting each constant into the equation the result is E = E degree - 0.0592V/n log_10 Q What is the value for the temperature, T, in kelvins? Express your answer to three significant figures and include the appropriate units. What is the value for n? Express your answer as an integer and include the appropriate units (i.e. enter mol for moles). Calculate the standard cell potential for Mg (s) + Fe^2+ (aq) rightarrow Mg^2+(aq) + Fe(s) Express your answer to three significant figures and include the appropriate units.

Explanation / Answer

B. 25 degree Celsius is Actually equals to 298.15 Kelvin. In three significant figures, it is 298 Kelvin.

C. The value of n is the number of electrons being transferred from anode (oxidation electrode) to cathode (reduction electrode). n can only be calculated if the reaction is provided. The one given in part D has the value of n=2 since Mg is getting oxidized releasing 2 moles of electrons and Fe(+2) is taking up those electrons to get reduced.

D. For the standard reduction potential of the complete cell we need to know the reduction potentials of half cells first, i.e reduction half and oxidation half.

Ecell= EFe2+/Fe -EMg/Mg2+ = -0.44 - (-2.37) Volts = 1.93V (in three significant figures)

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