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Fundamental chemical concepts

Word and balanced equations

Chemical equations show what happens in a reaction. In general, we write:

reactants → products

The reactants are the substances that react together. The products are the substances produced in the reaction. Individual substances are separated by a plus sign.

Word equations

A word equation gives the names of the substances involved in a reaction. For example:

copper + oxygen → copper(II) oxide

Copper and oxygen are the reactants, and copper(II) oxide is the product.

Balanced equations

Balanced equations give the symbols and formulas of the substances involved in a reaction. In the example above, if we just replace the words shown above with the correct chemical formulas, we will get an unbalanced equation, as shown here:

Cu + O2    →    CuO

To make things equal, we need to adjust the number of units of some of the substances until we get equal numbers of each type of atom on both sides of the arrow.

Here is the balanced symbol equation:

2Cu + O2    →    2CuO

You can see that we now have two copper atoms and two oxygen atoms on each side. This matches what happens in the reaction.

Two atoms of copper react with two atoms of oxygen to form two molecules of copper oxide

Here are some other examples of balanced equations. Check that you understand why they are balanced.

  • Mg + Cl2    →    MgCl2
  • 2Na + Cl2    →    2NaCl
  • 4Fe + 3O2    →    2Fe2O3
  • 4Na + O2    →    2Na2O
  • 2Na + 2H2O    →    2NaOH + H2.

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