This definitions covers Key Definitions within Exothermic Reactions for GCSE Chemistry. Revise Exothermic Reactions in Energy Changes for GCSE Chemistry with 20 exam-style questions and 14 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 6 of 12 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
📖 Key Definitions
Exothermic reaction: A reaction that transfers energy from the reacting chemicals to the surroundings, causing the temperature of the surroundings to increase. The products have less energy than the reactants.
Energy profile (reaction profile): A diagram showing how the energy of the reactants and products changes during a reaction. Shows reactants, products, activation energy peak, and ΔH.
Activation energy (Ea): The minimum energy that colliding particles must have to react. Even exothermic reactions need this initial energy "push" to break bonds in the reactants.
ΔH (enthalpy (energy change)): The overall energy change in a reaction. For exothermic reactions, ΔH is NEGATIVE (e.g., ΔH = −400 kJ/mol), showing energy is released to surroundings.
Surroundings: Everything outside the reaction — the water, container, air, and nearby objects that gain or lose heat during the reaction.
Practice questions for Exothermic Reactions
In an exothermic reaction, energy is transferred:
Explain, in terms of bond breaking and bond making, why combustion is an exothermic reaction.