i havent understood the basic concept and use of elingham diagram. plz.. explain it  simply how to check whch one will be reduced and which one oxidised??

Hi,

Ellingham diagrams follow from the Second Law of Thermodynamics [ΔG = ΔH - TΔS].

The Ellingham diagram plots the Gibbs free energy change (ΔG) for the oxidation reaction versus the temperature.

If two metals are present, two equilibriums have to be considered, so that the metal with the more negative ΔG reduces, the other oxidizes.

For example: Consider the following Ellingham diagram:

At 1073 K, the increasing order of reducing powers of the given metals is as follows.

Cu < Fe < Zn < Mg

In the given plots, it is observed that at 1073 K, the (Mg, MgO) line lies below the (Zn, ZnO) line, (Fe, FeO) line and (Cu, Cu₂O)) line. Therefore, ∆G°_{(Mg, MgO)} is lower than the value of ∆G°_{(Zn, ZnO)} which is lower than ∆G°_{(Fe, FeO)}, and ∆G°_{(Cu, Cu2O)}. Lower the ∆G° value, higher will be the reducing power. Hence, at 1073 K, Mg is a better reducing agent than Zn, Fe and Cu.

 

Hope this helps.

Cheers!