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GATE 2023 MT – Question 14

Metallurgical Thermodynamics · Reaction equilibria and Ellingham diagrams · 1 mark · Multiple choice

At one atmosphere, iron and nickel oxidise according to:

$2\mathrm{Fe}+\mathrm O_2\rightleftharpoons2\mathrm{FeO},\quad\Delta G^\circ=-527400+128T$ J.

$2\mathrm{Ni}+\mathrm O_2\rightleftharpoons2\mathrm{NiO},\quad\Delta G^\circ=-471200+172T$ J.

Temperature $T$ is in kelvin. Identify the correct statement.

  1. Fe can reduce NiO at all temperatures
  2. Fe can reduce NiO only above 1000 𝐾
  3. Ni can reduce FeO at all temperatures
  4. Ni can reduce FeO only above 1000 𝐾

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Correct answer: (A) Fe can reduce NiO at all temperatures

Explanation

Subtract nickel oxidation from iron oxidation. For $2\mathrm{Fe}+2\mathrm{NiO}\to2\mathrm{FeO}+2\mathrm{Ni}$, $\Delta G^\circ=(-527400+128T)-(-471200+172T)=-56200-44T$ J. This is negative for all positive temperatures within the supplied expressions.

Thus Fe reduces NiO, **A**.