Molten magnesium chloride can be decomposed into its elements by passage of an electric current according to the reaction
MgCl2(l)→Mg(l)+Cl2(g)
For this reaction under standard conditions at 298K, the standard cell potential is −2.71V. Faraday’s constant is 9.648×104C mol−1.
(a) Calculate the standard Gibbs free-energy change, in kilojoules per mole of MgCl2 decomposed, for the reaction above.
(b) A commercial electrolytic cell operates with an overall electrical efficiency of 80%. Calculate the minimum magnitude of the applied potential difference that must be maintained across the cell to sustain electrolysis under standard conditions.
(c) Classify the cell as galvanic or electrolytic under the conditions described. Support your answer by referring to the numerical values calculated in parts (a) and (b).
(d) State whether the decomposition of molten MgCl2 is thermodynamically spontaneous under standard conditions and explain how your answer relates to the need for an external power source.