The Equations for the formation of two oxides are
From the Ellingham diagram the two curves of these oxides formation intersect each otherat a certain point. The corresponding value of ∆G° becomes zero for the reduction of MgO by aluminium metal,
→ From the above information the reduction of MgO by Al metal cannot occur below this temperature (1665K) instead, Mg can reduce Al2O3 to Al below 1665 K.
→ Al–Metal can reduce MgO to Mg above 1665K because ∆G° for Al 2O3 is less compared to that of MgO.