Ellingham Diagram
A plot of the standard free energy of formation of metal oxides against temperature, used to choose a reduction route.
Formula / equation
ΔG° = ΔH° − TΔS°
Unit
kJ/mol
In depth
Each metal gives a nearly straight line, and any metal whose line lies below another's can reduce that oxide at that temperature. The carbon monoxide line slopes downward and eventually crosses almost all the others, which is why carbon reduction works for so many metals at high temperature.
Examples in the real world
The carbon line crossing the iron line near 700 °C, making blast furnace reduction thermodynamically possible.