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An Ellingham diagram shows curves for a metal oxide and for carbon combustion reactions, with four characteristic temperatures T1 < T2 < T3 < T4 marked. How many of the following statements about the diagram are correct? (A) Carbon can reduce the metal oxide (carbon being oxidised to CO2) only above temperature T3. (B) Carbon can reduce the metal oxide (carbon being oxidised to CO) at temperatures above T1. (C) Carbon monoxide can reduce the metal oxide (CO being oxidised to CO2) at temperatures above T3. (D) Carbon can reduce the metal oxide (carbon being oxidised to CO2) below temperature T2. (E) T4 represents the melting point of the metal.

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

In a standard Ellingham diagram, statements (B) and (C) are typically correct: the C->CO curve (steep negative slope) crosses and lies below the metal oxide curve above a certain temperature (here T1), and CO->CO2 can also reduce the metal oxide above a crossover temperature T3. Statements A, D, and E are generally incorrect as stated.

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