Answer to Question #133074 in General Chemistry for Frederick Jude Evangelista

Question

The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting, that is, the conversion of ZnS to ZnO by heating:
2ZnS(s)+3O_2 (g)→2ZnO(s)+2SO_2 (g) ∆H=-879 kJ/mol
Calculate the heat evolved (in kJ) per gram of ZnS roasted.

Answer 1

From conditions, heat evolved is 879 kJ per 2 moles ZnS, molar mass of ZnS is 97.5 g/mole. Heat evolved per 1 g of ZnS is:

879/(2*97.5) = 4.508 kJ per gram