Extraction of Metals - Result Question 9
####9. With respect to an ore, Ellingham diagram helps to predict the feasibility of its
(2019 Main, 8 April I)
(a) electrolysis
(b) zone refining
(c) vapour phase refining
(d) thermal reduction
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Solution:
- With respect to an ore, Ellingham diagram helps to predict the feasibility of its thermal reduction. It is a graph representation of Gibbs energy change versus absolute temperature.
Gibbs energy $\left(\Delta G^{\circ}\right)$ versus $T$ plots (schematic) for the formation of some oxides (Ellingham diagram)
Generally, the diagram consists of plots of $\Delta G^{\circ}$ versus $T$ for the formation of oxides of elements
$$ 2 x M(s)+O _2(g) \longrightarrow \underset{\text { Thermal reduction product }}{2 M _x O(s)} $$
In this reaction, amount of gas decreases thus, randomness decreases. Hence, $\Delta S$ becomes negative. Therefore, the value of free energy increases with increase in temperature. There is a point in a curve below which $\Delta G$ is negative. So, $M _x O$ is stable. Above this point, $M _x O$ will decompose on its own.
