2/9/2024 0 Comments Ellingham diagram explanation![]() Carbon dioxide (CO2) has a practically temperature-independent formation free energy but carbon monoxide (CO) has a negative slope and crosses the CO2 line near 700 ☌.The Al (aluminium oxidation) line is found to be lower than the Fe (ferrous oxidation) line (formation of Fe2O3). The lower the line in the Ellingham diagram is, the more stable a metal’s oxide is.Very unstable oxides, such as Ag2O and HgO, are easily thermally broken. As the temperature rises, the stability of metallic oxides decreases.S is proportional to the slope and is roughly constant with temperature. In Ellingham diagrams, curves for the synthesis of metallic oxides are often straight lines with a positive slope.As a result, even processes projected to be favourable by the Ellingham diagram can be delayed. The study is thermodynamic in nature and does not take into account reaction kinetics. The illustrations are helpful in anticipating how an ore will be converted to its metal content.The use of Ellingham diagram in metallurgy is to estimate the temperature of equilibrium between a metal, its oxide and oxygen - and by extension, interactions between a metal and sulphur, nitrogen and other non-metals. → Thus, coke can act as reducing agent for the reduction of metal oxide into metal and CO gas is evolved.Harold Ellingham created the first of these diagrams in 1944. It can also be understood with the help of Ellingham diagram given in fig. Thus from this discussion we can conclude that carbon will behave as reducing agent only when it changes into carbon monooxide during reduction process. ![]() But in case (c) the value of ∆S° becomes -ve as number of gaseous moles in reactants are larger than the number of gaseous moles in products. → It means ∆G° also becomes more negative as carbon is involved in the reduction of metal oxide. Now in case (b) there is increase in entropy i… ∆S° = +ve. Therefore change in Gibb’s free energy (AGR) is also zero ie, it remains constant during the reaction. → From above given reactions, it is clear that in case (a), there is no change in entropy i.e., ∆S° = 0 because the volume of O 2 and CO 2 gases are same. When it shows reduction then following reactions take place: → Reducing nature of Carbon (Coke): As it is well know that carbon acts as reducing agent. → Reducing nature of Coke (Carbon) and Carbon monooxide → Thus, from the above disucssion it is clear that at the bottom of the furnace where the temperature is above 1073 K, the reduction of Fe 2O 3 is done by carbon or coke i.e., carbon will behave as reducing agent while at the top part of the furnace where the temperature is below 1073 K, the reduction of Fe 2O 3 is done by carbon mono oxide i.e., at the top CO will behave as reducing agent. It means below 1073 K temperature, Fe 03 can be reduced by CO as(4,6°) will become negative for the reaction. → But in Ellingham diagram, we can observe that below 1073 K, the value of ∆G° for the formation of CO, from CO is more negative than the value of ∆G° for the formation of Fe 2 O 3 ∆G° (Fe → Fe 2O 3) > ∆G° (CO – CO. Hence, the ∆G° for the reaction will become positive so below 1073 K temperature, the reduction of Fe 2O 3 by Cis not possible. → Below 1073 K temperature, the value of ∆G° for the formation of CO 2 is less negative than the value of ∆G° for the formation of Fe0g. Thus above 1073 K temperature, carbon or coke can reduce the haematite because the (∆ rG°) for the reaction becomes more negative. Above 1073K temperature, the value of ∆G° for the formation of Fe, og is less negative than the value of ∆G° for the formation of CO from C. ![]() → Three curves cross each other at 1073 K. These three curves are represented in figure 6.6. In Ellingham diagram, there are three curves which illustrate the following reactions : Reduction of Haematite : Ellingham diagram can easily explain the reduction of haematite. Application of Ellingham Diagram Chemistry Notes
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