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Predict the conditions under which (a) Aluminium might be expected to reduce magnesia. (b) Magnesium could reduce alumina. |
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Answer» Solution :The conditions under which : Ellingham diagram is USED to predict thermodynamic feasibility of reduction of oxides of one metal by another metal. Any metal can reduce the oxides of other metals that are located above it in the Ellingham diagram. In the Ellingham diagram, for the fomation of magnesia (magnesium oxide) occupy lower position that a aluminium oxide. Therefore aluminium cannot be used to reduce the oxides of magnesium (magnesia). Above 1623K, AL can reduce MgO to Mg, so that `Delta_(r) G^(0)` becomes negative and the process becomes thermodynamically feasible. `3MgO + 2Al OVERSET(1623K)rarr Al_(2)O_(3) + 3Mg` (b) 1. `(4)/(3) Al + O_(2) rarr (2)/(3) Al_(2)O_(3)` 2. `2MG + O_(2) rarr 2MgO` At the point of intersection of the `Al_(2)O_(3)` and MgO curve in Ellingham diagram. `Delta G^(@)` becomes zero for the reaction: `(2)/(3) Al_(2)O_(3) + 2Mg rarr 2MgO + (4)/(3) Al` |
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