Balancing Chemical Equations

This lesson teaches you the systematic method for balancing chemical equations as required by the Edexcel GCSE Combined Science specification (1SC0). You will practise writing balanced symbol equations with state symbols and develop confidence with a wide range of equation types.

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Why Must Equations Be Balanced?

Because of the law of conservation of mass:

• The same number of each type of atom must appear on both sides of the equation.
• We balance equations by placing numbers (coefficients) in front of formulae — we NEVER change the formulae themselves.

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State Symbols

Every balanced equation should include state symbols to show the physical state of each substance:

Symbol	Meaning
(s)	Solid
(l)	Liquid
(g)	Gas
(aq)	Aqueous (dissolved in water)

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The Systematic Method for Balancing

Follow these steps every time:

Step 1: Write the correct formulae for all reactants and products (do NOT change these).

Step 2: Count the number of each type of atom on both sides.

Step 3: Balance one element at a time by adjusting coefficients.