Answer: an oxide is easier to reduce than the corresponding sulfide.
- A sulfur is more valuable and recovered as a byproduct
- B roasting is always cheaper than a direct reduction
- C an oxide is easier to reduce than the corresponding sulfide
- D sulfides cannot be melted at any practical temperature
Correct answer: C. an oxide is easier to reduce than the corresponding sulfide
Explanation: The ΔG of formation of CO<sub>2</sub>/CO is more negative than that of CS<sub>2</sub>, so carbon reduces oxides readily but not sulfides; hence sulfides are first converted to oxides by roasting.
An Ellingham diagram plots ΔG° of oxide formation against temperature for different metals; whichever line is LOWER (more negative ΔG°) at a given temperature reduces the oxide of any metal whose line sits above it - the basis of carbon reduction (Fe, Zn) vs electrolytic reduction (Al, Mg, Na) decisions.
Concept context
The science of extracting metals from ores and refining them for use. Covers concentration methods, reduction techniques, refining processes, and the thermodynamic principles that govern metal extraction.