Given below are two statements related to Ellingham diagram:
Statement I : Ellingham diagrams can be constructed for formation of oxides, sulfides and halides of metals.
Statement II : It consists of plots of Δ_f H⁰ vs T for formation of oxides of elements.
In the light of the above statements, choose the most appropriate answer from the options given below:

Solution

Chemistry ma’am · 4 steps

Read the y-axis carefully: an Ellingham diagram plots free energy, not enthalpy, against temperature.

1. Statement I. The Ellingham idea works for any reaction of a metal with a fixed amount of a non-metal. Diagrams are drawn for oxides, sulfides and halides alike, so Statement I is correct.
2. What is plotted. Each line shows Δ_f G° (per mole of O₂ for oxides) against T. Free energy is what tells you whether a reduction is feasible, since a reaction can go only when Δ G° is negative.

   Δ G° = Δ H° - T Δ S°

3. Statement II. Statement II says Δ_f H° vs T. That is wrong. The slope of each line is -Δ S°, which is why most oxide lines rise with temperature: gaseous O₂ is used up, so Δ S° is negative.
4. So. Statement I is correct and Statement II is incorrect, which is option (c).

The idea to keep. Ellingham diagram means Δ G° vs T. The slope is -Δ S°, and a lower line means a more stable compound, so that metal can reduce the oxide of a metal whose line lies above it.

Answer from the NTA final answer key. Solution by PrepWiser.