### GCSE Chemistry

Quantitative Chemistry
Chemical Changes
Energy Changes
Organic Chemistry
Chemical Analysis
Earth and Atmospheric Science
Using Resources

# Balancing Chemical Equations

The law of conservation states that no atoms are lost or gained during a chemical reaction. This means that the total number of atoms must remain constant before and after the reaction.

To write a balanced chemical equation, we start by writing the reactants (the substances that react) on the left-hand side of the arrow and the products (the substances that are produced) on the right-hand side.

Next, we make sure that there is the same number of atoms of each element on both sides of the arrow. If not, we add coefficients (numbers in front of the chemical formulas) to balance the equation.

For example, let’s look at the reaction between oxygen (O2) and hydrogen (H2) to form water (H2O):

Let’s look at another example that involves sulphuric acid (H2SO4) reacting with sodium hydroxide (NaOH).

## Example

Balance the equation below and add state symbols.

H2SO4 + NaOH Na2SO4 + H2O

1. Check the number of atoms of each element on each side. In this case, we can see that the number of hydrogen atoms on the right side of the arrow (3H) is different from the number on the left side (2H).

2. To balance the hydrogen atoms, add a coefficient of 2 in front of the water molecule (H₂O). The equation now looks like this:

H₂SO₄ + NaOH → Na₂SO₄ + 2H₂O

• However, it increased the number of hydrogen atoms and the number of oxygen atoms

3. Now check the number of sodium atoms on both sides. To balance the sodium atoms, add a coefficient of 2 in front of the sodium hydroxide molecule (NaOH). The balanced equation now looks like this:

H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O

• This also balanced the number of oxygen atoms

4. Finally, if required, add state symbols to indicate the physical state of each substance. In this case, sulphuric acid and sodium hydroxide are both in aqueous (aq) form, while water is in its liquid (l) form. The final balanced equation is:

H₂SO₄ (aq) + 2NaOH (aq) → Na₂SO₄ (aq) + 2H₂O (l)

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