The factor of  $\mathrm{\Delta }G$ values are important in metallurgy. The $\mathrm{\Delta }G$ values for the following reactions at 800°C are given as

${\mathrm{S}}_2\left(s\right)+2{\mathrm{O}}_2\left(g\right)\to 2{\mathrm{SO}}_2\left(g\right),\mathrm{\Delta }G=-544kJ$

$2Zn\left(s\right)+S_2\left(s\right)\to 2ZnS\left(s\right),\mathrm{\Delta }G=-293kJ$

$2\mathrm{Zn}\left(s\right)+{\mathrm{O}}_2\left(g\right)\to 2\mathrm{ZnO}\left(s\right),\mathrm{\Delta }G=-480kJ$

The  $\mathrm{\Delta }G$ for the reaction, 

$2\mathrm{ZnS}\left(\mathrm{s}\right)+3{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{ZnO}\left(\mathrm{s}\right)+2{\mathrm{SO}}_2\left(\mathrm{g}\right)$ Will be