Answer: the minimum temperature above which carbon can reduce that oxide.
- A the boiling point of that metal
- B the melting point of that oxide
- C the minimum temperature above which carbon can reduce that oxide
- D the temperature at which the metal oxide decomposes by itself
Correct answer: C. the minimum temperature above which carbon can reduce that oxide
Explanation: Above the crossover point the carbon line lies below the metal-oxide line, so the coupled reaction has a negative ΔG, meaning carbon can reduce that oxide only above this temperature.
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.