What happens when (a) ${\mathrm{ZnCO}}_3$is heated in the absence of oxygen? (b) a mixture of ${\mathrm{Cu}}_2\mathrm{O}$ and ${\mathrm{Cu}}_2\mathrm{S}$is heated?

The reaction of Zinc carbonate in absence of oxygen:

• When zinc carbonate $\left({\mathrm{ZnCO}}_3\right)$ is heated in absence of air, carbon dioxide $\left({\mathrm{CO}}_2\right)$ and zinc oxide $\left(\mathrm{ZnO}\right)$ are formed.
• Calcination is the process that involves the reduction of carbonate ores to oxides in the absence of oxygen.
• The chemical equation can be depicted as:

${\mathrm{ZnCO}}_3\left(\mathrm{aq}\right)\stackrel{∆}{\to }\mathrm{ZnO}\left(\mathrm{s}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$

Reaction between Copper oxide and Copper sulfide:

• When a mixture of copper oxide $\left({\mathrm{Cu}}_2\mathrm{O}\right)$ and copper sulfide $\left({\mathrm{Cu}}_2\mathrm{S}\right)$ is heated, pure copper $\left(\mathrm{Cu}\right)$ is formed along with the liberation of sulfur dioxide $\left({\mathrm{SO}}_2\right)$.
• The chemical equation can be depicted as:

$2{\mathrm{Cu}}_2\mathrm{O}\left(\mathrm{s}\right)+{\mathrm{Cu}}_2\mathrm{S}\left(\mathrm{s}\right)\stackrel{∆}{\to }6\mathrm{Cu}\left(\mathrm{s}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right)$