Question

Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?

• A. the magnitude of $\Delta G_{f}^{o}$ of the sulphide is greater than those for $CS_{2}$ and $H_{2}S$
• B. the $\Delta G_{f}^{o}$ is negative for roasting of sulphide ore to oxide
• C. roasting of the sulphide to the oxide is thermodynamically feasible
• D. carbon and hydrogen are suitable reducing agents for metal sulphides

Answer 1

Answer: (D)

The standard free energies of formation $\left(\Delta G_{f}^{o}\right)$ of most of the sulphides are greater than those of $CS_{2}$ and $H_{2}S$ . Hence, neither carbon nor hydrogen can reduce metal sulphides to metal. The standard free energies of formation of oxides are much lower than those of $SO_{2}$ . Therefore, oxidation of metal sulphides to metal oxides is thermodynamically favourable. Hence sulphide ore is roasted to the oxide before reduction.