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Reactant - GCSE Chemistry Definition

Reviewed by: Richard Boole

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In GCSE Chemistry, a reactant is a substance present at the start of a chemical reaction. Reactants change during the reaction to form new substances called products.

For example:

Hydrogen + Oxygen → Water

In this reaction, hydrogen and oxygen are the reactants, and water is the product.

Understanding reactants is important for predicting what products will form, how much will be made, and how the reaction will proceed.

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Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

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