Chemical reactions
Atoms are rearranged in a chemical reaction. The substances that:
- react together are called the Substances present at the start of a chemical reaction.
- are formed in the reaction are called the A substance formed in a chemical reaction.
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:
Image caption, The test tube is partly filled with a mixture of iron and sulfur
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Iron sulfide, the compound formed in the reaction, has different properties to the elements from which it is made. The table compares the properties of iron, sulfur and iron sulfide:
| Iron | Sulfur | Iron sulfide | |
| Type of substance | Element | Element | Compound |
| Colour | Silvery grey | Yellow | Black |
| Is it attracted to a magnet? | Yes | No | No |
| Reaction with hydrochloric acid | Hydrogen formed | No reaction | Hydrogen sulfide formed, which smells of rotten eggs |
| Type of substance | |
|---|---|
| Iron | Element |
| Sulfur | Element |
| Iron sulfide | Compound |
| Colour | |
|---|---|
| Iron | Silvery grey |
| Sulfur | Yellow |
| Iron sulfide | Black |
| Is it attracted to a magnet? | |
|---|---|
| Iron | Yes |
| Sulfur | No |
| Iron sulfide | No |
| Reaction with hydrochloric acid | |
|---|---|
| Iron | Hydrogen formed |
| Sulfur | No reaction |
| Iron sulfide | Hydrogen sulfide formed, which smells of rotten eggs |
The atoms in a compound are chemically joined together by strong forces called The chemical link that holds molecules together.. 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.