M (s) + O (g) ------ ( ) 2y 2xy The above reduction may be carried out with carbon. In this case, the reducing agent carbon may be oxidised to either CO or CO . C + O CO (g) ------ ( ) 2C + O 2CO (g) ------ ( ) If carbon monoxide is used as a reducing agent, it is oxidised to CO as follows, 2CO + O 2CO (g) ------ ( ) A suitable reducing agent is selected based on the thermodynamic considerations. We know that for a spontaneous reaction, the change in free energy (ΔG) should be negative.
Therefore, thermodynamically, the reduction of metal oxide [equation ( )] with a given XII U1 Metallurgy - XII U1 Metallurgy - - - - - reducing agent [Equation ( ), ( ) or ( )] can occur if the free energy change for the coupled reaction. [Equations ( ) & ( ), ( ) & ( ) or ( ) & ( )] is negative. Hence, the reducing agent is selected in such a way that it provides a large negative ΔG value for the coupled reaction. .
. Ellingham diagram 2Mg + O → 2MgO 2Ca + O → 2CaO /3Al + O → /3Al O /3Cr + O → /3Cr O 2Mn + O → 2MnO 2Zn + O → 2ZnO 2Fe+ O → 2FeO 2Ni + O → 2NiO 4Cu + O → 2Cu O C + O → CO 2C + O → 2CO – – – – – – – – – – – – 2Mg + O → 2MgO 2Ca + O → 2CaO /3Al + O → /3Al O 2Mn + O → 2MnO 2Zn + O → 2ZnO 2Fe+ O → 2FeO 2Ni + O → 2NiO 4Cu + O → 2Cu O ∆ G° = RT In p O2 / kJmol – O C + O → CO