Chemical reactions

Atoms are rearranged in a chemical reaction. The substances that:

  • react together are called the reactants
  • are formed in the reaction are called the products

No atoms are created or destroyed in a chemical reaction. This means that the total mass of the reactants is the same as the total mass of the products. We say that mass is conserved in a chemical reaction.

Making iron sulfide

The reaction between iron and sulfur is often used to study elements and compounds. Iron sulfide is the compound produced in the reaction. The slideshow shows what happens in this reaction:

Test tube is filled with a mixture of iron and sulfur

The test tube is partly filled with a mixture of iron and sulfur

Iron atom symbols are added to sulfur atom symbols to produce the compound iron sulfide, which contains both atom symbols mixed upThe atoms of iron and sulfur are rearranged to form iron sulfide in the chemical reaction

Iron sulfide, the compound formed in the reaction, has different properties to the elements from what it is made. The table compares the properties of iron, sulfur and iron sulfide:

IronSulfurIron sulfide
Type of substanceElementElementCompound
ColourSilvery greyYellowBlack
Is it attracted to a magnet?YesNoNo
Reaction with hydrochloric acidHydrogen formedNo reactionHydrogen sulfide formed, which smells of rotten eggs

The atoms in a compound are chemically joined together by strong forces called bonds. This is why the properties of a compound are different from the elements it contains, and why you can only separate its elements using another chemical reaction. Separation methods like filtration and distillation will not do this.