Exothermic Reactions

Energy changes are at the heart of chemistry. Every chemical reaction involves a transfer of energy, and understanding whether energy is released or absorbed is a fundamental part of the Edexcel GCSE Chemistry (1CH0) specification. In this lesson you will learn what exothermic reactions are, explore key examples, understand reaction profile diagrams for exothermic reactions, and carry out a core practical measuring the temperature change during a neutralisation reaction.

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What Is an Exothermic Reaction?

An exothermic reaction is a chemical reaction that transfers energy to the surroundings. The surroundings get hotter and there is a measurable temperature increase.

In an exothermic reaction:

• The energy released by forming new bonds in the products is greater than the energy needed to break bonds in the reactants.
• The excess energy is transferred to the surroundings, usually as heat (thermal energy).
• The products have less energy than the reactants.
• The overall energy change (ΔH) is negative.

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Examples of Exothermic Reactions