1) Calculate the standard free-energy change at 25 ?C for the following reaction

Question

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

Mg(s)+Fe^2+(aq)?Mg^2+(aq)+Fe(s)

Answer should be in J

2) Calculate the standard cell potential at 25 ?C for the reaction

X(s)+2Y+(aq)?X^2+(aq)+2Y(s)

where ?H? = -615kJ and ?S? = -297J/K .

Answer should be in V

3) Calculate ?G?rxn and E?cell for a redox reaction with n = 3 that has an equilibrium constant of K = 28.

4)A Cu/Cu2+ concentration cell has a voltage of 0.23V at 25 ?C. The concentration of Cu2+ in one of the half-cells is 1.6

Explanation / Answer

1)

Mg -----> Mg2+ + 2e- Eo = +2.37 V
Fe2+ + 2e- -----> Fe Eo = -0.44 V
Mg + Fe2+ -----> Mg2+ + Fe Eo(cell) = 1.93 V

dGo = -nFEo
dGo = -2 mol x 96,500 C/mol x 1.93 J/C = -372,000 J
= -372 kJ

2)

X(s)+2Y+(aq)?X^2+(aq)+2Y(s)

dG = dH - TdS
dGo = -nFEo
dGo = -2 mol x 96,500 C/mol x Eo
dGo=-615kJ+298x297

dGo=-526494J=-2x96500xEo

Eo=2.728V

3)

Gibbs free energy of reaction dGr an equilibrium constant K are related as
dGr = - RdTln(K)
where R is the universal gas constant and T is the thermodynamic temperature

At standard conditions the temperature is
T

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