(i) At about 1000ºC, lines cross and thus at this temperature zinc and carbon have equal affinity for oxygen.

(ii) In Ellingham diagram all three oxidation curves for the carbon system lie above that for oxidation of zinc, until a temperature of approximately 1000ºC is reached. At this point C is thermodynamically capable of reducing ZnO to Zn. The overall equation for reduction is

ZnO(s) + C(s) ⎯→ Zn(g) + CO(g)

(iii) FeO(s) + C(s) ⎯→ Fe(s/l) + CO (g) ..............

FeO(s) ⎯→ Fe(s) + O 2 (g) [ Δ G (FeO, Fe) ] ..............

C(s) + O 2 (g) ⎯→ CO(g) [ Δ G (C, CO) ] ..............

Δ G (C, CO) + Δ G (FeO, Fe) = Δ r G ..............

In Δ Gº vs T plot representing reaction , the plot goes upward and that representing the change C → CO (C, CO) goes downward. At temperatures above 1073K (approx.), the C, CO line comes below the Fe,FeO line

[ Δ G (C, CO) < Δ G (Fe, FeO) ]. So in this range, coke will be reducing the FeO and will itself be oxidised to CO. In a similar way the reduction of Fe 3 O 4 and Fe 2 O 3 at relatively lower temperatures by CO can be explained on the basis of lower lying points of intersection of their curves with the CO, CO 2 curve in the given figure.

2ZnS + 3O 2 ⎯→ 2ZnO + 2SO 2 ; ZnS + 2O 2 ⎯→ ZnSO 4 ; ZnSO 4 2ZnO + 2SO 2 + O 2

The reduction of zinc oxide is done using coke. The temperature in this case is higher than that in case of copper because ZnO line crosses C → CO line at higher temperature than that of CuO.