When a stoichiometric amount of Iron and Sulfur is ignited, Iron Sulphide is formed in a spectacular way. Here is how to do the experiment:
- Fe(s) + S(s) –> FeS(s)
- The reaction is highly exothermic and releases 100kJ per mole of Iron Sulfide
Prepare the reaction
- Mix both powders very well. Additionally, you can show your students that iron is a magnetic powder and can be separated from the sulfur.
- Pour the contents on a fireproof, disposable surface and ignite using a hot steel rod.
- Afterwards you can show, that the product (Iron sulfide) is no longer attracted to a magnet
Sulfur and Iron Reaction
It is assumed that the main reaction that occurs is:
Fe(s) + S(s) –> FeS(s)
but the system is probably much more complex than that. The standard enthalpy of formation of FeS is -100 kJ/mol. The iron and sulfur are present in the reaction mixture in roughly equimolar quantities. Though the color of the product is not very different from the reaction mixture, the change in physical properties can be demonstrated by allowing the product to cool, removing it and bringing a magnet close to demonstrate that the product is not magnetic, whereas one of the reactants (iron) is. (Be careful though, sometimes unreacted bits of iron remain in the product, especially around the edges.)