Exothermic and Endothermic Reactions
Temperature evidence, energy transfer, reaction profiles, activation energy and bond-energy calculations.
How to study for GCSE Chemistry
Move between particle models, equations, calculations, observations and data; practise the specific required activities and paper structure named by your exam board.
Core concepts
Concept 1
An exothermic reaction transfers energy to the surroundings, while an endothermic reaction takes in energy from the surroundings.
Exam cue: State whether the measured temperature refers to the surroundings before classifying the reaction.
Concept 2
A reaction profile shows reactant and product energy levels and the activation-energy barrier, which is not the overall energy change.
Exam cue: Read vertical energy differences carefully on a reaction profile.
Concept 3
Breaking bonds requires energy and making bonds releases energy; the net energy change depends on the balance of both.
Exam cue: Calculate total energy for bonds broken minus total energy released by bonds formed.
Risk pitfalls and guardrails
Saying exothermic means the reacting chemicals contain no energy.
Guardrail: Do not rely on a memorised keyword alone: preserve charges, ratios, units and conditions, and keep single Chemistry separate from Combined Science.
Equating activation energy with the reaction's overall energy change.
Guardrail: Do not rely on a memorised keyword alone: preserve charges, ratios, units and conditions, and keep single Chemistry separate from Combined Science.
Reversing the energy signs for bond breaking and bond making.
Guardrail: Do not rely on a memorised keyword alone: preserve charges, ratios, units and conditions, and keep single Chemistry separate from Combined Science.
Memory anchors
Exothermic
Energy is transferred from the reacting system to the surroundings.
Endothermic
Energy is transferred from the surroundings into the reacting system.
Activation energy
The minimum energy particles need for a successful reaction.
Bond breaking
Requires energy.
Bond making
Releases energy.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A reaction vessel warms without external heating. Which definition describes the energy transfer?
A dissolving process cools its beaker. Which definition describes this change?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 247 UK exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”