Free-energy change, %u0394 G %u2218 , is related to cell potential, E %u2218 , b

Question

Free-energy change, %u0394G%u2218, is related to cell potential, E%u2218, by the equation

%u0394G%u2218=%u2212nFE%u2218

where n is the number of moles of electrons transferred and F=96,500C/(mol e%u2212) is the Faraday constant. When E%u2218 is measured in volts, %u0394G%u2218 must be in joules since 1 J=1 C%u22C5V.

Mg(s)+Fe2+(aq)%u2192Mg2+(aq)+Fe(s)

Calculate the standard cell potential at 25 %u2218C for the reaction

X(s)+2Y+(aq)%u2192X2+(aq)+2Y(s)

where %u0394H%u2218 = -917kJ and %u0394S%u2218 = -203J/K .

Mg(s)+Fe2+(aq)%u2192Mg2+(aq)+F

Explanation / Answer

2)

dGo = dHo -TdS

d G= -917- (298) (-.203 Kj/K)
= -856.506 Kj/k
dGo = -nFEo =-856.506,

-856.506 kJ = -2 moles of electrons (96.5kJ/mol-ev)(Eo)
Eo = 4.4378 volts

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