The choice of a reducing agent in the extraction of a particular case depends on thermodynamic factor. Explain.

Explanation

The choice of the a reducing agent in a particular case depends on thermodynamic factor. This fact can be explained by considering the following exaples.
`rarr` out of Cand CO , carbon nonoxide (CO) is a better reducting agent at 673K.
`rarr` At 983K (or) CO , carbon nonoxide (CO) is a better reducting agent at 673K .
`rarr` The above observations are form Ellingham diagram.
Zinc is not extracted from Zinc oxide through reduction using CO.
Explanation :
`2Zn+O_(2)rarr2ZnO,DeltaG^(@)=-650KJ`
`2CO+O_(2)rarr2CO_(2),DeltaG^(@)=-450KJ`
`2ZnO+2COrarr2Zn+2CO_(2')DeltaG^(@)=200KJ`
`DeltaG^(@)` = Positive indicatis that the reaction is not feasible.
The extraction of copper from pyrites is more difficult than that from its oxide ore through reduction.
Explanation : Pyrites is `(Cu_(2)S)` cannot be reduced by carbir (or) hydrogent because the standar free energy of formation `(DeltaG^(@))` of `Cu_(2)S` is greater then those of `CS_(2)` and `H_(2)S`
`{:(2Cu_(2)S+Crarr4Cu+CS_(2)),(Cu_(2)S+H_(2)rarrCu+H_(2)S):}}" Not fessible"`
`rarr` The `DeltaG^(@)` of copper oxide is less than that of `CO_(2)`
`therefore` The sulphide ore is firts converted to oxide by roasting and then reduced .
`2Cu_(2)S+3O_(2)underset("Heat")overset("Roasting")rarr2Cu_(2)+2SO_(2)`
`2Cu_(2)+O+Crarr4Cu+CO_(2)["feasible"].`
The following are the conditions that Al might be expected to reduce MgO. The Equations for the formation of two oxides are
`(4)/(3)Al_((s))+O_(2(g))rarr(2)/(3)Al_(2)O_(3(s))`
`2Mg_((s))+O_(2(g))rarr2MgO_((s))`
From the Ellingham diagram the two curves of these oxides formation intersect each otherrat a certain point. The corresponding value of `DeltaG^(@)` becomes zero for the reduction of MgO by aluminium metal,
`2MgO_((s))+(4)/(3)hArr2Mg_((s))+(2)/(3)Al_(2)O_(3_(s))`
From the above information the reduction of MgO by Al metal cannot occur below this temperature (1665 K) instead ,Mg can reduce `Al_(2)O_(3)` to al below 1665K.
`rarr` Al- Metal can reduce MgO to Mg above 1665 K because `DeltaG^(@)` for `Al_(2)O_(3)` is less compared to that of MgO.
`3MgO_((s))+2Al_((s))overset(T gt 1665K)rarrAl_(2)O_(3(s))+2Mg_((s))`