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#ELLINGHAM DIAGRAMS FREE#

Using this property, reduction of metals may be performed as a double redox reaction at relatively low temperature. Moreover, when carbon reacts with oxygen it forms gaseous oxides carbon monoxide and carbon dioxide, therefore the dynamics of its oxidation is different from that for metals: its oxidation has a more negative ΔG with higher temperatures. Carbon is available cheaply as coal, which can be rendered to coke). In industrial processes, the reduction of metal oxides is effected using carbon. At the point of intersection the Gibbs energy is 0(zero), below this point the Gibbs energy is 0 and so, the oxides are unstable. Reduction with using a certain reductant is possible at the intersection point and higher temperatures where the ΔG line of the reductant is lower on diagram than the metallic oxide to be reduced.

The intersection of two lines imply the equilibrium of oxidation and reduction reaction between two substances.

Hence metallic aluminum can reduce iron from iron oxide into metallic iron, aluminum itself oxidizing into aluminum oxide.

#ELLINGHAM DIAGRAMS FREE#

A substance whose Gibbs free energy of formation is lower (ΔG line lower on diagram) at given temperature, will reduce one whose free energy of formation is higher on the diagram.

According to Boudouard reaction, carbon monoxide is the dominant compound in higher temperatures, and the higher the temperature, the more efficient reductant carbon monoxide also is.

The formation enthalpy of carbon dioxide (CO 2) is almost a temperature-independent constant, while that of carbon monoxide (CO) has negative slope.

Highly unstable oxides like Ag 2O and HgO easily undergo thermal decomposition.

Stability of metallic oxides decrease with increase in temperature.

The greater the gap between any two lines, the greater the efficiency of the reducing agent.

For example, the Ellingham diagram for Al is found to be below Fe 2O 3.

The lower the position of a metal in the Ellingham diagram, the greater is the stability of its oxide.

Curves in the Ellingham diagrams for the formation of metallic oxides are straight lines with a positive slope.

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

At a sufficiently high temperature, the sign of ΔG may invert (becoming negative) and the oxide can spontaneously reduce to the metal.Īs with any chemical reaction prediction based on purely energetic grounds the reaction may or may not take place spontaneously on kinetic grounds if one or more stages in the reaction pathway have very high Activation Energies E A. In the temperature ranges commonly used, the metal and the oxide are in a condensed state (liquid or solid) with the oxygen gaseous, the reactions may be exothermic or endothermic, but the ΔG of the oxidation always becomes more negative with lower temperature, and thus the reaction becomes more probable statistically. The Ellingham diagram plots the Gibbs free energy change (ΔG) for the oxidation reaction versus the temperature. ΔG is the Gibbs Free Energy Change,ΔH is the Enthalpy Change and ΔS is the Entropy Change] Ellingham diagram for high temperature oxidationĮllingham diagrams follow from the second law of thermodynamics and are a particular graphical form of it.