Search any question & find its solution
Question:
Answered & Verified by Expert
Is it true that under certain conditions, Mg can reduce \(\mathrm{Al}_2 \mathrm{O}_3\) and \(\mathrm{Al}\) can reduce \(\mathrm{MgO}\) ? What are those conditions?
Solution:
2295 Upvotes
Verified Answer
Below \(1966 \mathrm{~K}, \Delta_{\mathrm{f}} \mathrm{G}^{\circ}\) curve for the formation of \(\mathrm{SiO}_2\) lies above the \(\Delta_f \mathrm{G}^{\circ}\) curve for the formation of \(\mathrm{MgO}\), therefore, at temperatures below \(1966 \mathrm{~K}, \mathrm{Mg}\) can reduce \(\mathrm{SiO}_2\) to metallic silicon.
\(\begin{aligned}
&\mathrm{SiO}_2+2 \mathrm{Mg} \stackrel{1966 \mathrm{~K}}{\longrightarrow} 2 \mathrm{MgO}+\mathrm{Si} ; \\
&\Delta_{\mathrm{r}} \mathrm{G}^{\circ}=\text { negative }
\end{aligned}\)
Above \(1966 \mathrm{~K}, \Delta_{\mathrm{f}} \mathrm{G}^{\circ}\) curve for the formation of \(\mathrm{SiO}_2\) lies below the corresponding curve for the formation of \(\mathrm{MgO}\). Therefore, above \(1966 \mathrm{~K}\), silicon can reduce \(\mathrm{MgO}\) to \(\mathrm{Mg}\).
\(\mathrm{Si}+2 \mathrm{MgO} \stackrel{>1966 \mathrm{~K}}{\longrightarrow} \mathrm{SiO}_2+\mathrm{Mg}\)
\(\begin{aligned}
&\mathrm{SiO}_2+2 \mathrm{Mg} \stackrel{1966 \mathrm{~K}}{\longrightarrow} 2 \mathrm{MgO}+\mathrm{Si} ; \\
&\Delta_{\mathrm{r}} \mathrm{G}^{\circ}=\text { negative }
\end{aligned}\)
Above \(1966 \mathrm{~K}, \Delta_{\mathrm{f}} \mathrm{G}^{\circ}\) curve for the formation of \(\mathrm{SiO}_2\) lies below the corresponding curve for the formation of \(\mathrm{MgO}\). Therefore, above \(1966 \mathrm{~K}\), silicon can reduce \(\mathrm{MgO}\) to \(\mathrm{Mg}\).
\(\mathrm{Si}+2 \mathrm{MgO} \stackrel{>1966 \mathrm{~K}}{\longrightarrow} \mathrm{SiO}_2+\mathrm{Mg}\)
Looking for more such questions to practice?
Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.