Question

Ellingham diagrams are mainly used to determine:

• A. Phase equilibrium
• B. Oxide stability
• C. Reaction kinetics
• D. Diffusion coefficients

Hint:

The lower a line is on the Ellingham diagram, the more stable the oxide is, meaning it is harder to reduce but has a stronger affinity for oxygen.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks about the primary utility of an Ellingham diagram in metallurgical engineering.
Ellingham diagrams are thermodynamic plots widely used in pyrometallurgy to study the reduction of metal oxides, sulfides, and halides.

Step 2: Key Formula or Approach:
An Ellingham diagram plots the standard Gibbs free energy of formation (\( \Delta G^\circ \)) of oxides (usually normalized per mole of \( \text{O}_2 \)) as a function of absolute temperature (\( T \)):
\[ \Delta G^\circ = \Delta H^\circ - T\Delta S^\circ \]
where:
\( \Delta H^\circ \) is the standard enthalpy of formation, and
\( \Delta S^\circ \) is the standard entropy of formation.

Step 3: Detailed Explanation:

• Oxide Stability Assessment: The relative position of the curves on the diagram indicates the thermodynamic stability of the respective oxides.
A lower position on the diagram (more negative \( \Delta G^\circ \)) corresponds to a more stable oxide because more energy is released during its formation.

• Reducing Agent Selection: The diagram helps determine which reducing agent (such as Carbon, Carbon Monoxide, or another metal) can successfully reduce a specific metal oxide at a given temperature.
A metal whose line lies lower on the diagram can reduce the oxide of a metal whose line lies higher on the diagram.

• Limitations: The Ellingham diagram is purely thermodynamic and does not provide information regarding reaction kinetics (Option C) or diffusion parameters (Option D).
It also does not directly represent multi-component phase equilibria (Option A).


Step 4: Final Answer:
Hence, the primary use of Ellingham diagrams is to determine oxide stability, which aligns with Option (B).