Question

Is it true that under certain conditions, Mg can reduce SiO₂ and Si can reduce MgO? What are those conditions?

Answer 1

\[\ce{Mg_{(s)} + \frac{1}{2} O2_{(g)} -> MgO_{(s)}[\Delta G_{Mg, MgO}]}\]

\[\ce{Si_{(s)} + O2_{(g)} -> SiO2_{(s)} [\Delta G_{Si,SiO_2}]}\]

The temperature range in which \[\ce{[\Delta G_{Mg,MgO}]}\] is lesser than \[\ce{[\Delta G_{Si,SiO_2}]}\], Mg can reduce SiO₂ to Si.

\[\ce{2Mg + SiO2 -> 2MgO + Si}\]; ΔG° = −ve

On the other hand, the temperatures range in which \[\ce{[\Delta G_{Si,SiO_2}]}\] is less than \[\ce{[\Delta G_{Mg,MgO}]}\], Si can be reduce MgO to Mg.

\[\ce{SiO2 + 2Mg -> SiO2 + 2Mg}\]; ΔG° = −ve

The temperature at which Δ_fG 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.