Question
The Gibb's energy for the decomposition of Al2O3 at 500o C is as follow
2/3 Al2O3 → 4/3 Al + O2;
ΔrG = +960 kJ mol-1
The potential difference needed for the electrolytic reduction aluminium oxide (Al2O3) at 5000 C is at least
-
4.5 V
-
3.0 V
-
2.5 V
-
5.0 V
Solution
C.
2.5 V
at anode
2O2- +4e- →O2] x 3
at cathode
Al3+ → Al +3e-] x4
Net reaction
4Al +6O2- → 3O2 +4Al
Or
4/3Al +2O2- → O2 +4/3Al
n= 12/3 = 4
ΔGo = -nFEo
ΔGo = +960 kJ mol-1
= 960 x 1000 J mol-1
n=4
F =96500 Coulomb
960 x 1000 = -4 x 96500 x Eo
