A standard galvanic cell is constructed so that the overall cell reaction is as given below where M is an unknown metal. 2 Al3 + (aq) + 3 M (s) 3 M2 + (aq) + 2 Al (s) If ΔG° = - 411 kJ for the overall cell reaction, identify the metal used to construct the standard cell.

magnesium metal

Explanation:

According to the redox reaction equation, six electrons were transferred hence n=6 and F = Faraday's constant 96500C. ∆G° is given hence E°cell can easily be calculated as follows:

From ∆G° = - nFE°cell

E°cell = - ∆G°/nF = - (-411*10^3/96500*6)

E°cell = 0.7098V

But for Al3 + (aq) / Al (s) half cell, E° = - 1.66V from standard table of reduction potentials.

E°cell = E°cathode - E°anode but Al3 + (aq) / Al (s) half cell is the cathode

Hence

E°anode=E°cathode - E°cell

E°anode = - 1.66-0.7098 = - 2.37V

This is the reduction potential of Mg hence the anode material was magnesium metal