GCSE Chemistry - Balancing Equations | Writing Word & Symbol Equations (2026/27 exams)

Chemical equations are essential for understanding chemical reactions. These can be represented as word equations or symbol equations. Word equations describe reactions using the names of reactants (starting materials) and products (formed substances). For example, methane burning in oxygen produces carbon dioxide and water.

Symbol equations use chemical symbols for each molecule. For instance, methane (CH4) plus oxygen (O2) yields carbon dioxide (CO2) and water (H2O). It's crucial to remember that some elements like oxygen, chlorine, and nitrogen exist as diatomic molecules (e.g., O2, Cl2, N2) and must be written as such in equations.

A chemical equation must be balanced, meaning it has the same number of each type of atom on both sides of the arrow (reactants and products). An unbalanced equation, like the initial CH4 + O2 → CO2 + H2O example, shows an unequal number of atoms, necessitating adjustments.

When balancing, you cannot change the small subscript numbers as this alters the chemical substance itself (e.g., changing O2 to O3 changes oxygen to ozone). Instead, you must change the large numbers (coefficients) in front of the elements or compounds, which represent the quantity of that substance. Also, only whole numbers can be used as coefficients, not fractions.

To balance CH4 + O2 → CO2 + H2O, start with an element like oxygen. Adjust the coefficient in front of O2 to increase oxygen atoms on the left. Then, adjust the coefficient in front of H2O to balance hydrogen and oxygen atoms on the right. Through trial and error, the balanced equation becomes CH4 + 2O2 → CO2 + 2H2O, ensuring one carbon, four hydrogens, and four oxygens on both sides.

For H2SO4 + NaOH → Na2SO4 + H2O, it's recommended to balance less common elements first. Sulfur is already balanced. To balance sodium, place a '2' in front of NaOH. Then, re-count all atoms and adjust the coefficient for H2O to balance hydrogen and oxygen. The final balanced equation is H2SO4 + 2NaOH → Na2SO4 + 2H2O, resulting in four hydrogens, one sulfur, six oxygens, and two sodiums on each side.