This definitions covers Key Definitions within Endothermic Reactions for GCSE Chemistry. Revise Endothermic Reactions in Energy Changes for GCSE Chemistry with 20 exam-style questions and 14 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. 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
Endothermic reaction: A reaction that absorbs energy from the surroundings, causing the temperature of the surroundings to decrease. The products have more energy than the reactants.
Thermal decomposition: A type of endothermic reaction in which a compound is broken down into simpler substances by heating. It requires continuous energy input. Example: CaCO₃ → CaO + CO₂.
ΔH (enthalpy (energy change)): The overall energy change in a reaction. For endothermic reactions, ΔH is POSITIVE (e.g., ΔH = +178 kJ/mol), showing energy is absorbed from surroundings.
Photosynthesis: An endothermic reaction in which plants absorb light energy (from the Sun) and use it to convert carbon dioxide and water into glucose: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
Reversible reaction: A reaction that can go in both directions. If the forward reaction is endothermic, the reverse reaction is exothermic (and vice versa) — the same amount of energy is involved, just in opposite directions.
Practice questions for Endothermic Reactions
In an endothermic reaction, energy is:
Explain why a sports cold pack becomes cold when activated.