Answer
4.51 kJ/g
Work Step by Step
879 kJ is evolved when 2 mol of ZnS roasted.
439.5 kJ is evolved per mol of ZnS roasted.
As the molar mass of ZnS= 97.474 g/mol, we can say that
439.5 kJ is evolved when 97.474 grams of ZnS is roasted.
$\implies$ heat evolved per gram= $\frac{439.5\,kJ}{97.474\,g}$
$=4.51\,kJ/g$
