Predict conditions under which Al might be expected to reduce MgO.

Explanation

The two equations are :
`2Mg + O_2 to 2MgO`
`4/3 Al + O_2 to 2/3 Al_2 O_3`
It is clear from Ellingham diagram (fig.) that `Delta G^@` vs T plot for Mg, MgO is below `Delta G^@` vs T plot for Al. Therefore, Al cannot reduce MgO to Mg. However m at the point of intersection (corresponding to temperature 1623K) , the `DeltaG^@` for the combined reaction becomes zero. After this point (1623 K), Mg - MgO curve, is higher than that for Al- `Al_2 O_3` curve. Thus, Al can reduce MgO at temperature higher than 1623 K. But there are practical difficulties at attain higher temperatures.