Question

The smelting of Zinc Oxide (obtained from roasted ZnS) happens __ the boiling point of Zinc metal

Answer 1

Zinc boils at ${920}^{0}C$ and the smelting happens at a significantly higher ${1300}^{0}C$. This is because of the following side reaction during smelting:

$C{O}_2\left(g\right)+C$ $\to$ $2CO\left(g\right)△H>0$ endothermic

This reaction lowers the temperature thus impeding the vapourization (of Zinc)