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Question
Is it true that under certain conditions, Mg can reduce SiO2 and Si can reduce MgO? What are those conditions?
Solution
`Mg_(s) + 1/2 O_(2(g)) -> MgO(s)[triangleG_(Mg, MgO)]`
`Si_(s) +O_(2(g)) -> SiO_(2(s))[triangleG_(Si.SiO_2)]`
The temperature range in which `triangleG_(mg,MgO)` is lesser than `triangleG_(Si,SiO_2)`, Mg can reduce SiO2 to Si.
`2Mg + SiO_2 -> 2MgO+ Si; triangleG^theta = -ve`
On the other hand, the temperatures range in which `triangleG_(Si,SiO_2)` is less than `triangleG_(Mg, MgO)`, Si can reduce MgO to Mg.
`SiO_2 + 2Mg -> SiO_2 + 2Mg; triangleG^theta = -ve`
The temperature at which ΔfG curves of these two substances intersect is 1966 K. Thus, at temperatures less than 1966 K, Mg can reduce SiO2 and above 1966 K, Si can reduce MgO.
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