Advanced Topic 691 of 1102 Inorganic Chemistry
Ellingham Diagram
Plots free energy of oxide formation against temperature to choose reducing agents.
In-depth explanation of Ellingham Diagram
An Ellingham diagram plots the standard Gibbs free energy change for forming a metal oxide, per mole of oxygen, against temperature. Each oxide gives a roughly straight line, and a lower line means a more stable oxide. A reducing agent can reduce any oxide whose line lies above the line for its own oxide, because the coupled reaction then has a negative free energy change. The carbon line slopes downward, so carbon can reduce many oxides at high temperature. The diagram is therefore used to choose reducing agents and smelting temperatures.
Going deeper: Ellingham Diagram
Key ideas: Plots delta G for oxide formation per mole O2 against temperature. Slope is -delta S, positive for most metals as the gas is consumed. A metal oxide is reduced by an element whose line lies below it at that temperature. C to CO has a negative slope, crossing lines for FeO, ZnO at high temperature, enabling carbon reduction above that point (about 700 C for FeO). Al2O3 line lies far below, so Al reduces many oxides, but carbon cannot reduce it below 2000 C.
Common mistakes and connections: Students read the diagram for rate; it shows only thermodynamic feasibility. Slope changes at melting or boiling points, due to entropy change. Do not compare lines drawn per mole of different gases. Mg and Al lines are below, thus they are better reducing agents. Links to Gibbs energy, delta G = delta H - T delta S, and metallurgy.
Visualization of Ellingham Diagram
Ellingham lines: the carbon line crosses below zinc oxide at high temperature so C can reduce ZnO, but never reaches the very stable Al2O3. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Carbon reduces zinc oxide at high temperature, giving zinc vapour and carbon monoxide.
Frequently asked questions about Ellingham Diagram
What is Ellingham Diagram?
Plots free energy of oxide formation against temperature to choose reducing agents.
Is Ellingham Diagram a beginner, intermediate or advanced topic?
Ellingham Diagram is a advanced topic in Inorganic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Ellingham Diagram?
Study these earlier topics in Inorganic Chemistry first: Ore Concentration, Roasting and Calcination, Smelting.
What comes after Ellingham Diagram?
The next topics in Inorganic Chemistry are Thermite Reaction and Refining of Metals.
Can I practise Ellingham Diagram with quizzes?
Yes. The interactive lesson includes a self-check question on Ellingham Diagram, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Ellingham Diagram fits in Inorganic Chemistry
Ellingham Diagram is topic 76 of 113 in Inorganic Chemistry.