How do I calculate reaction free energy?

Calculate the standard free-energy change at 25 Celsius for the following reaction:?

• Mg (s)+ Fe^{2+}(aq) -----> Mg^{2+)(aq)+Fe (s) Express your answer numerically in joules. INFO: Free-energy change, \Delta G^\circ, is related to cell potential, E^\circ, by the equation \Delta G^ \circ = -nFE^\circ where n is the number of moles of electrons transferred and F =96,500\; \rm C/(mol ~e^-) is the Faraday constant. When E^\circ is measured in volts, \Delta G^ \circ must be in joules since 1 \rm ~J = 1 ~C \cdot V.

• Answer:

  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