JEE Main 2021 · 27 July · morning · Single correct · +4 / −1
The statement is incorrect about Ellingham diagram is
- (a) provides idea about the reaction rate.
- (b) provides idea about free energy change.
- (c) provides idea about changes in the phases during the reaction.
- (d) provides idea about reduction of metal oxide.
Answer and solution
Answer (a) provides idea about the reaction rate.
Solution
Chemistry ma’am · 2 steps
An Ellingham diagram is pure thermodynamics: it tells you if a reduction can happen, never how fast.
- What is plotted. An Ellingham diagram plots Δ_f G° for forming metal oxides (per mole of O₂) against temperature. Every point on it is a free energy value, so it can only answer thermodynamic questions.
Option What the diagram shows Verdict (a) reaction rate Nothing. Δ G° says whether a reaction is feasible, not how fast it goes. Rate is kinetics. incorrect (b) free energy change Δ G° is the quantity on the y-axis. correct (c) phase changes A sudden change in slope marks melting or boiling of the metal or oxide, because Δ S changes there. correct (d) reduction of metal oxide A metal or C/CO whose line lies lower can reduce an oxide whose line lies above it. correct - So. The diagram says nothing about speed, so the incorrect statement is (a).
The idea to keep. Ellingham diagrams give feasibility, the best reducing agent, the minimum temperature and phase changes. They never give kinetics: a negative Δ G° can still mean a very slow reaction.
Answer from the NTA final answer key. Solution by PrepWiser.