Ellingham Diagram

The Ellingham diagram graph shows the soundness of a composite varies with temperature. This technique is usually accustomed to confirm however simple it's to cut back iron oxides and sulfides. The primary of those statues was fictionalized by Harold Ellingham in 1944. 

In metals, the Ellingham diagram is employed to calculate the equilibrium temperature between the metal, its oxide, and oxygen, also because of the interaction between iron and sulfur, nitrogen, and different non-metals. Diagrams are accustomed to predict how a metal will regenerate into a containing metal. analysis could be about thermodynamic surroundings and doesn't embrace reaction mechanics.

Ellingham diagram is a plot between Gibbs free energy and temperature. It helps us to know the best reducing agent for a particular metal oxide and sulfides. As we know – 

∆G° = ∆H°-T.∆S°

If  ∆G°<0, then the reaction will be spontaneous.

If ∆G°=0, the reaction will be at equilibrium 

If ∆G°>0, then the reaction will be non-spontaneous. 

In metallurgy, we want metal oxides and sulfides to get reduced to get pure metal at low cost. For this purpose, metal oxides and sulfides are reduced by best suitable reducing agents through spontaneous reactions. In this Ellingham diagram plays an important role to select a best suitable reducing agent. Thus, in a way, the Ellingham diagram relates thermodynamics and metallurgy. 

Suppose for a reaction A + B \[\rightarrow\] C

Values above the ∆G°=0 will be positive while below the ∆G°=0 will be negative. General representation is shown below for your better understanding – 

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If ∆G°<0 for A + B \[\rightarrow\] C then this reaction will be spontaneous. 

If we Reverse the Reaction –

C \[\rightarrow\] A + B, then ∆G°>0 so the reaction will be non-spontaneous. 

Now if ∆G°>0 for A + B \[\rightarrow\] C then this reaction will be non – spontaneous.

If we Reverse the Reaction –

C \[\rightarrow\] A + B, then ∆G°<0 so the reaction will be spontaneous. 

For example, suppose a graph is given for following reactions of metal oxides –

\[ 2Ag_{2}O ∆ \rightarrow  4Ag + O_{2} \]

\[ 2HgO ∆ \rightarrow  2Hg + O_{2} \]

\[ 2ZnO ∆ \rightarrow 2Zn + O_{2} \]

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Ellingham diagram area unit, a picture of a thermodynamic conception. The Ellingham diagram shows Gibbs free energy modification (G) because the temperature operates in every chemical reaction method. At temperatures unremarkably accustomed to compare completely different reactions, iron and chemical compound area unit in an exceedingly solid state (solid or liquid), whereas chemical element could be a gas with the best molar entropy.

The curves for the assembly of aluminiferous oxides in the Ellingham diagram area unit typically straight lines with an immediate volume. Slope is said to be temperature and is nearly constant. Once the chemical compound of the metal is strong, its line decreases within the Ellingham diagram. The soundness of aluminiferous chemical compounds decreases because the temperature rises. Temperature degradation is simple on unstable oxides like silver 2O and HgO.

Carbon dioxide (CO₂) has nearly free radicals that burn free energy, however monoxide (CO) incorporates a negative impact and exceeds the CO₂ line at 700 °C. monoxide is that the dominant carbon chemical compound at high temperatures (approximately 700 °C), betting on the Boudouard reaction, and therefore the higher the temperature (above 700 ° C), the less CO₂ works best.

When the curves of the 2 metals at a given temperature area unit compared, the sturdy free {gibbs|Gibbs|Josiah Willard Gibbs, the chemist} of low chemical reaction, reduces the chemical compound by the free Gibbs production power within the drawing. The larger the gap between any 2 lines, the less effective the chemical related to the lower line. The equilibrium of chemical reaction reduction is indicated by the crossing of 2 lines. At temperatures on top of the junction, wherever the G-line of the reducer is lower within the diagram than that of the aluminiferous chemical compound to be reduced, a discount of that reducer is taken into account.

The location of the road within the Ellingham diagram shows the chemical compound stability as an operation of temperature. Fine metals, like Pt and gold, have a high reaction once viewed upwards as a result of their oxides area unit speedily depleted and unstable. Metals grow additional active because the line goes down, creating it tougher to cut back oxides.

Ellingham diagrams are unit wide utilized in the sphere of extractive science, wherever they assist in choosing the suitable reductant for the assorted ore within the extraction method, also because of the refinement and setting of the metal production stage. It conjointly helps to scrub the metal, particularly in eliminating trace parts. Ellingham drawings show that atomic number 1 will convert iron oxides into iron alone; that could be a direct reduction mechanism for the formation of iron.

In the graph, the Ellingham curve is less than that of the many different metals, like steel. This is often a decent suggestion that everyone on top of the graph can be used as an Associate in Nursing oxidizer. As a result corundum is stable, it's utilized in a thermite method to extract metal.

At around a thousand K, the Ellingham diagram of FeO and CO constructions meets. The carbon fiber is on top of the metal line below this temperature, which indicates that FeO is additional stable than CO and so the reduction cannot operate thermodynamically at this distance. However, on the far side a thousand K, the carbon fiber falls below the metal line, permitting North American countries to use coke as a reductant. Sequent calculations of free energy make sure that the reduction has thermodynamically helpful advantages.

Ellingham diagrams are a unit created solely on the premise of thermodynamic principles. Provides data regarding the likelihood of thermodynamic reactions. It doesn't give data regarding response rate. What is more, it doesn't give a sign of the chance of further responses occurring.

Applications of Ellingham Diagram

Few applications of Ellingham diagram are listed below –

1.It is used to evaluate the ease of reduction of metal oxides and sulfides. 

2.In metallurgy it is used to predict the equilibrium temperature between metal, oxide and oxygen. It also predicts the reaction of metals with nitrogen, sulfur and nonmetals.

3.By Ellingham diagram we can predict the condition under which an ore can be reduced to its metal.

4.It is used for finding the best suitable reducing agent for reduction of metal oxides.

5.It is used to find out the feasibility of thermal reduction of an ore.

As we know, the Ellingham curve for aluminum lies below most metals such as Fe, Cr etc. which indicates that Al can be used as the reducing agent for oxides of all these metals. 

Limitations of Ellingham Diagram 

It has few limitations as well which are listed below –

1.It ignores the reaction kinetics meaning it does not provide any information about the kinetics of the reduction reaction.

2.The analysis is thermodynamic in nature, it means the reactions which are predicted by the Ellingham diagram can be very slow. 

3.It assumes that the reactants and products are in equilibrium, but it is not always the case.

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