Ellingham diagrams are a particular graphical form of the principle that the thermodynamic feasibility of a reaction depends on the sign of ΔG, the Gibbs free energy change, which is equal to ΔH−TΔS, where ΔH is the enthalpy change and ΔS is the entropy change. Hence, element below in Ellingham diagram can reduce oxide of element above it.
C can reduce FeO at 600ºC.
