Question

Free-energy change, ΔG∘, is related to cell potential, E∘, by the equation

ΔG∘=−nFE∘

where n is the number of moles of electrons transferred and F=96,500C/(mol e−) is the Faraday constant. When E∘ is measured in volts and can be determined from half-reaction potentials as given in the table below. ΔG∘ must be in joules since 1 J=1 C⋠V.

Reduction half-reaction	E∘ (V)
Ag+(aq)+e−→Ag(s)	0.80
Cu2+(aq)+2e−→Cu(s)	0.34
Sn4+(aq)+4e−→Sn(s)	0.15
2H+(aq)+2e−→H2(g)	0
Ni2+(aq)+2e−→Ni(s)	−0.26
Fe2+(aq)+2e−→Fe(s)	−0.45
Zn2+(aq)+2e−→Zn(s)	−0.76
Al3+(aq)+3e−→Al(s)	−1.66
Mg2+(aq)+2e−→Mg(s)	−2.37

Part A

Calculate the standard free-energy change at 25 ∘C for the following reaction using the table in the introduction:

Mg(s)+Fe2+(aq)→Mg2+(aq)+Fe(s)

Express your answer numerically in joules.

ΔG∘ =

J

Part B

Calculate the standard cell potential at 25 ∘C for the reaction

X(s)+2Y+(aq)→X2+(aq)+2Y(s)

where ΔH∘ = -923 kJ and ΔS∘ = -123 J/K .

Express your answer numerically in volts.

E∘ =

V