Thermodynamic factors help us in choosing a suitable reducing agent for the reduction of a particular metal state as described below.

From Ellingham diagram, it is evident that metals for which the standard free energy of formation of their oxides is more negative can reduce those metal oxides for which the standard free energy of formation of their respective oxides is less negative. In other words, any metal will reduce the oxides of other metals which lie above in the Ellingham Diagram because the standard free energy change of the combined redox reaction will be negative by any amount of equal to the difference in Δ _fG⁰ of the two metal oxides. Hence, both Al, Zn can reduce FeO to Fe, but Fe cannot reduce Al₂O₃ to Al and ZnO to Zn.