JEE Main 2021 · 25 February · morning · Single correct · +4 / −1
Ellingham diagram is a graphical representation of :
- (a) ΔG vs P
- (b) ΔG vs T
- (c) (ΔG - TΔS) vs T
- (d) ΔH vs T
Answer and solution
Answer (b) ΔG vs T
Solution
Chemistry ma’am · 4 steps
Feasibility of reduction changes with heating, so Ellingham plots Δ G° against T.
- What is plotted. An Ellingham diagram plots the standard Gibbs energy change Δ G° for forming an oxide (per mole of O₂) on the y-axis against temperature T on the x-axis. Each metal or reducing agent gets its own line.
Δ G° = Δ H° - TΔ S°
- Why straight lines. Over a wide range of temperature, Δ H° and Δ S° stay nearly constant. So Δ G° against T is a straight line with slope -Δ S° and intercept Δ H°.
- Why it is useful. A reducing agent can reduce a metal oxide at temperatures where its own line lies below that metal's line, because the combined Δ G° is then negative. Reading this off needs Δ G° on one axis and T on the other.
- So. The Ellingham diagram is a plot of Δ G vs T, option (b).
The idea to keep. Ellingham diagram means Δ G° of oxide formation against T. Slope is -Δ S°, and a lower line can reduce the oxide of a higher line at that temperature.
Answer from the NTA final answer key. Solution by PrepWiser.