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GATE 2019 MT – Question 16

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

Standard oxide-formation free energies vary with temperature as shown. Which statement is correct?

Diagram for GATE 2019 MT question 16
  1. AO is a gas.
  2. BO is a gas.
  3. A reduces BO above T₁.
  4. B reduces AO below T₁.

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Show answer and explanation

Correct answer: (B) BO is a gas.

Explanation

The slope of an Ellingham line is −ΔS°. The BO-formation line has negative slope, implying a positive reaction entropy despite oxygen consumption. Formation of gaseous BO explains this increase. Above T₁, BO has the lower formation free energy, so A cannot reduce BO there; below T₁ the opposite reduction claim is also unfavourable. Thus B.

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