Answer: 700°C (Ellingham diagram crossover between C/CO line and Fe2O 3 line).
- A 700°C (Ellingham diagram crossover between C/CO line and Fe2O<sub>3</sub> line)
- B 0°C, the freezing point of water rather than any meaningful crossover temperature
- C 1500°C, far above the actual Ellingham crossover for this pair of lines
- D 25°C, ordinary room temperature with no special thermodynamic significance here
Correct answer: A. 700°C (Ellingham diagram crossover between C/CO line and Fe2O<sub>3</sub> line)
Explanation: The C→CO line on the Ellingham diagram crosses below the Fe→Fe2O<sub>3</sub> line at about 700°C; above this T, CO reduction of Fe2O<sub>3</sub> is spontaneous; the actual blast furnace operates at ~1500-1700°C for complete reduction.
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.