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प्रश्न
Predict conditions under which Al might be expected to reduce MgO.
उत्तर १
Above 1350°C, the standard Gibbs free energy of formation of Al2O3 from Al is less than that of MgO from Mg. Therefore, above 1350°C, Al can reduce MgO.
उत्तर २
The equations for the formation of the two oxides are
`4/3 Al(s) + O_2(s) -> 2/3 Al_2O_3(s)`
`2Mg(s)+O_2(s) -> 2MgO(s)`
`Double arrow`
If we look at the plots for the formation of the two oxides of the Ellingham diagram, we find that they intersect at certain point. The corresponding value of ΔG° becomes zero for the reduction of MgO by Al metal.
2MgO(s) + 4/3Al(s) ⇌ 2Mg(s) + 2/3Al2O3(s)
This means that the reduction of MgO by Al metal can occur below this temperature. Aluminium (Al) metal can reduce MgO to Mg above this temperature because Δ°G for Al2O3 is less as compared to that of MgO.
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