On the basis of Ellingham's diagram explain the principle of extraction of iron from its oxide ore.

Explanation

1. Thermodynamcs helps us to understand how coke reduces the oxides of iron. The Ellingham diagram for Fe.
` to FeOFe to Fe_(2)O_(3) to CO` and `CO to CO_(2)` are given above.
2. From the above Ellingham diagram, it is known that `Delta G^@` vs T plot for the reaction
`Fe to FeO` goes up and `C to CO` line joins the `Fe to FeO` line.
3. Above 1073K. `AG^@` of `C to CO` becomes less than `AG^@` of `Fe to FeO` and hence carbon itself is oxidized to carbon monoxide. Therefore, carbon becomes very good reducing agent which reduces FeO to Fe at the temperature range 900-1500K.
`FeO(s) + C(s) to Fe(s//I) + CO(g)`
4. At temperature below 800K, standard free energy change for `CO to CO_(2)` line is less than `Fe to Fe_(2)O` line. Therefore, carbon monoxide is the best reducing agent and is oxidised to carbon dioxide by reducing `Fe_(2)O_(3)` and `Fe_93)O_(4)` to Fe.
`3 Fe_(2)O_(3) + CO to 2Fe_(3)O_(4) + 4CO_(9)`.
`Fe_(3)O_(4) + 4CO to 3Fe + 4CO_(2)`.
`Fe_(2)O_(3) + CO to 2FeO + CO_(2)`
5. At temperature below 1073K, CO reduces FeO to Fe
`FeO to Fe +CO_(2)`.