Final answer:
To answer the student's question, divide the total heat evolved by the mass of ZnS that reacted which gives -4.51 kJ/g. However, this answer does not match any of the provided options, indicating a possible mistake in the question or options.
Step-by-step explanation:
The question asks to calculate the heat evolved per gram of ZnS roasted in the roasting process of zinc sulfide ore to zinc oxide. The chemical reaction provided is: 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g), ΔH = -879 kJ/mol. To find the heat evolved per gram of ZnS, we need to divide the total heat evolved by the total amount of ZnS that reacted. The molar mass of ZnS is 97.46 g/mol. Therefore, for 2 moles of ZnS (2 × 97.46 g = 194.92 g), the heat evolved is -879 kJ. To find the heat evolved per gram of ZnS, we divide -879 kJ by 194.92 g:
ΔH per gram of ZnS = -879 kJ / 194.92 g = -4.51 kJ/g
Since the options provided do not include this value, it seems there is a mistake either in the question or the options provided. If rounded according to significant figures or due to a potential typo in the question, the closest option presented is b. -439.5 kJ/g, which appears to be half the -879 kJ per mole value, but this would not be correct per gram, so there may be a misunderstanding or a typo in the question or the options given.