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At temperature above 1073K, coke can be ...

At temperature above 1073K, coke can be used to reduce FeO to Fe. How can you justify this reduction with Ellingham diagram ?

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The correct Answer is:
As per Ellingham diagram at temperature greater than `1073 K`
`DeltaG (C, C0) lt DeltaG (Fe, FeO)`. Hence coke can reduce `FeO` to `Fe`.
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For a sponaneous reaction, the free energy change must be negative, Delta G=Delta H-T Delta S, Delta H is the enthalpy change during the reaction. T is the absolute temperature, and Delta S is the change in entropy during the reaction. Consider a reaction such as the formation of an oxide M+O_(2) to MO Dioxygen is used up in the course of this reaction. Gases have a more random structure (less ordered) than liquid or solids. Consequently gases have a higher entropy than liquids and solids. In this reaction S (entropy or randomness) decreases, hence Delta S is negative. Thus, if the temperature is raised then T Delta S becomes more negative,Since, TDelta S is substracted in the equation, then Delta G becomes less negative. Thus, the free energy change increases with the increase in temperature. The free energy changes that occur when one mole of common reactant (in this case dioxygen) is used may be plotted graphically aginst temperature for a number of reactions of metals to their oxides. The following plot is called an Ellingham diagram for metal oxide. Understanding of Ellingham diagram is extremely important for the efficient extraction of metals. Which of the following elements can be prepared by heating the oxide above 400^(@)C ?

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Metals are extracted from their ores by a wide variety of techniques. The most common ores are oxides. Most metals are obtained by direct treatment of theirs ores with chemical agents, but the extraction of certain others require electrolysis. An example of the former type of process is the extraction of iron from its oxide, described by the following equation : Fe_(2) O_(3) + 3C rarr 2Fe + 3CO The relative ease of extraction of a metal from its oxide can be estimated using the Ellingham diagram, as shown in the figure. The diagram plots the free energies of formation of various oxides per mole of consumed oxygen as a function of absolute temperature. Which of the following best explains why the free energy of formation of Fe_(2)O_(3) becomes less negative as the temperature is increased.

ALLEN-METALLURGY-EXERCISE -04
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