Answer: Above 700°C, carbon (coke) can reduce Fe2O 3 spontaneously; below, it cannot.
- A Above 700°C, carbon (coke) can reduce Fe2O<sub>3</sub> spontaneously; below, it cannot
- B Metallic iron is instead able to reduce carbon oxides above this temperature
- C The carbon and iron oxide lines actually never cross on the diagram
- D Iron oxide spontaneously decomposes into free iron without any reducing agent
Correct answer: A. Above 700°C, carbon (coke) can reduce Fe2O<sub>3</sub> spontaneously; below, it cannot
Explanation: Where the C/CO line crosses below the Fe/Fe2O<sub>3</sub> line, Delta_G for the overall reduction becomes negative; that temperature is the minimum for coke reduction of iron oxide.
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.