Why is it advantageous to roast a sulphide ore to the oxide before reduction ?

Explanation

### Step-by-Step Solution:

1. **Understanding Roasting and Reduction**:
- Roasting is the process of heating a sulfide ore in the presence of oxygen to convert it into an oxide. Reduction is the process of removing oxygen from the oxide to obtain the pure metal.

2. **Thermodynamic Stability**:
- The standard free energy of formation (ΔF) of most sulfides is more negative than that of carbon disulfide (CS₂) and hydrogen sulfide (H₂S). This indicates that carbon and hydrogen cannot effectively reduce metal sulfides because their free energy values are not favorable for such a reaction.

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