Sulphur and iron in hydrochloric acid. Image 3 of 4. Sulphur does not react with hydrochloric acid, while the iron reacts to form iron (II) chloride and bubbles of hydrogen. This is part of a demonstration showing the differences between a chemical and a physical change. A mixture of iron and sulphur (a physical change) has different properties from iron sulphide, the compound formed when they react together (a chemical change). This can be demonstrated by their reactivity with hydrochloric acid. Images A500/596, A500/597 and A500/599 respectively show iron, sulphur and iron sulphide in hydrochloric acid.