GCSE Chemistry (Triple) Edexcel

Key Concepts: Chemical Equations

Understanding Chemical Equations

Chemical equations are a way of representing chemical reactions. They show the substances involved in the reaction - the reactants (on the left) and the products (on the right).

Symbols are used in chemical equations. The '+' in a chemical equation separates reactants or products from each other, and '→' indicates the direction of the reaction.

Some chemical reactions are reversible, and this is indicated in the chemical equation by a two-headed arrow (↔).

State symbols show the physical states of the substances at room temperature. (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous solution.

Balancing Chemical Equations

All chemical equations need to be balanced. This principle follows the law of conservation of mass, which says that no atoms are lost or made during a chemical reaction.

In a balanced chemical equation, the number and type of atoms is the same on both sides.

Molar coefficients in front of a chemical formula indicate the number of moles of that substance. They are used to balance the equation.

To balance an equation, start by balancing elements that appear in only one compound on each side.

If you end up with fractional coefficients while balancing, you can multiply all coefficients by the denominator of the fraction to make them whole numbers.

Sometimes, in complicated equations, polyatomic ions that stay intact during the reaction can be treated as single units for easier balancing.

Writing Chemical Equations

Writing chemical equations sometimes requires knowledge of the formulas for certain common compounds. For instance, the formula for water is H2O and for carbon dioxide, it's CO2.

Some reactions need a specific condition to occur, such as heat or pressure. These conditions are usually noted above or below the arrow. For instance, heat is often denoted as '∆'.

A Note on Practice

Remember, practise makes perfect so keep practising writing and balancing chemical equations. Starting with simple equations then proceeding to more complex ones is a good strategy.