text: The concept of plotting the free energies of reaction of various elements with a given gas-phase reactant may be extended beyond oxidation reactions. The original paper by Ellingham explicitly to the reduction of both oxygen and sulfur by metallurgical processes, and anticipated the use of such diagrams for other compounds, including chlorides, carbides, and sulfates. The concept is generally useful for studying the comparative stability of compounds across a range of partial pressures and temperatures. The construction of an Ellingham diagram is especially useful when studying the stability of compounds in the presence of a reductant. Ellingham diagrams are now available for bromides, chlorides, fluorides, hydrides, iodides, nitrides, oxides, sulfides, selenides, and tellurides.