Following method of extracting
Zn is based on thermodynamics
A :
2ZnS+3O2⟶2ZnO+2SO2B :
ZnO+C⟶Zn+COIf △Gof (standard free energies of formation, in kJmol−1 ) of ZnS=−205.4, ZnO=−318.0, SO2=−300.4 and of CO=−137.3
Free energy changes of the above reaction A and B (respectively) will be :