Learners need to be able to recognise different chemical reactions, including simple decomposition reactions at 11–14

This resource accompanies the Education in Chemistry article The beauty of a breakup, which provides everyday contexts for decomposition reactions.

  • Composite image showing the decomposition reactions student sheets and teacher notes.

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    Download the unscaffolded student worksheet as MS Word or pdf and the scaffolded student worksheet as MS Word or pdf.

    Download the teacher notes, including answers, as MS Word or pdf.

Learning objectives

  1. Identify decomposition reactions from a word equation or symbol equation.
  2. Use the law of conservation of mass to balance simple decomposition reactions.


Decomposition reactions are a key part of our everyday lives. The decomposition of hydrogen peroxide is responsible for bleaching hair, cleaning bathrooms and making paper white, while the decomposition of sodium hydrogen carbonate (baking soda) makes cakes rise and puts the bubbles in honeycomb.

Scientists are even looking to decomposition reactions to provide alternatives to fossil fuels, with the decomposition of water producing a cleaner source of energy for hydrogen-fuelled vehicles.

How to use the resources

Decomposition reactions allow lots of opportunities for practical work or demonstrations. Using these question sheets, learners can apply their knowledge to questions that link decomposition reactions to word equations, symbol equations and conservation of mass.

There are two versions of the worksheet. An unscaffolded version where learners can write the answers in their own words and a scaffolded version where learners can use the prompts, key words and fill-in-the-gap style questions to support their answers. The scaffolded version is denoted by the symbol ‘S’ in the document header. A challenge question is included at the end of both versions.

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