Ellingham diagram is plot of ∆GvvT. The criterion for the feasibility of a thermal reduction is that at a given temperature Gibbs energy change of a reaction must be negative. The change in Gibbs energy, ∆G for any process at any specified temperature is given by the equation ∆G=∆H−T∆S where ∆H= enthalpy change and ∆S= entropy change According to the ellingham diagram, any metal oxide with higher ∆G∘ has a tendency of getting reduced by the metal whose metal oxide has lower value of ∆G∘.