Sulphur reacts with iron by combining directly to form iron(II) sulfide when heated, in an exothermic reaction. This common chemical reaction demonstrates the direct synthesis of a compound from its elements.
Understanding the Reaction Process
When iron (Fe) and sulphur (S) are mixed and subjected to heat, a significant chemical transformation occurs. The provided reference clearly states: "On heating the reaction mixture, the sulfur melts and reacts with the iron exothermically to form iron(II) sulfide."
Here's a breakdown of the process:
- Initial State: Iron, typically in powder or filings form, is mixed with powdered sulphur.
- Heating: The mixture needs to be heated to initiate the reaction. As heat is applied, the sulphur melts first due to its lower melting point.
- Reaction Initiation: Once the sulphur melts, it becomes more reactive, allowing it to readily come into contact and combine with the iron particles.
- Exothermic Nature: The reaction is exothermic, meaning it releases heat energy. Once initiated, the reaction often becomes self-sustaining, continuing without external heating as the heat generated by the reaction itself fuels further reaction.
- Product Formation: The product of this reaction is iron(II) sulfide (FeS).
Chemical Equation
The balanced chemical equation for the reaction between iron and sulphur is:
Fe (s) + S (s) → FeS (s)
Where:
Fe (s)represents solid iron.S (s)represents solid sulphur.FeS (s)represents solid iron(II) sulfide.
Key Characteristics of the Reactants and Product
| Characteristic | Iron (Fe) | Sulphur (S) | Iron(II) Sulfide (FeS) |
|---|---|---|---|
| Appearance | Silvery-grey solid | Yellow solid (powder) | Dark grey/black solid |
| State at STP | Solid | Solid | Solid |
| Reactivity | Moderately reactive metal | Non-metal, reactive | Stable compound |
| Magnetic? | Yes (ferromagnetic) | No | No (the new compound is not attracted to a magnet) |
Practical Insights and Safety Considerations
This reaction is often performed in educational settings to demonstrate chemical change and the concept of exothermic reactions.
- Energy Release: The exothermic nature means the test tube or container holding the reaction mixture will become very hot.
- Safety Precaution: As highlighted in the reference, "The mineral wool plug in the mouth of the test tube prevents sulfur vapour escaping and possibly catching fire." Sulphur, when heated, can vaporize, and sulphur vapour is flammable. A mineral wool plug acts as a barrier, containing the vapor and preventing it from igniting or escaping into the environment.
- Formation of a New Substance: A clear indicator of a chemical reaction is the formation of a new substance with different properties. Unlike the initial mixture, iron(II) sulfide is a new compound with distinct chemical and physical properties (e.g., it is not attracted to a magnet, unlike iron).
