Chemical Energy Changes
Comparing exothermic and endothermic reactions, interpreting profiles and using bond energies and calorimetry evidence.
How to study for GCSE Combined Science
Build the three sciences as connected disciplines, practise mathematical and practical reasoning, then apply the common core to the exact tier and paper structure of your current specification.
Core concepts
Concept 1
Exothermic reactions transfer energy to surroundings; endothermic reactions take in energy from surroundings.
Exam cue: State the system and surroundings before interpreting temperature change.
Concept 2
Activation energy is the minimum energy barrier, shown between reactants and the peak of a reaction profile.
Exam cue: Use energy in minus energy out with the sign convention required by the question.
Concept 3
Breaking bonds requires energy and forming bonds releases energy; the balance determines overall energy change.
Targeted study blocks
Tier coverage
Foundation core with Higher-tier extensions
Higher-tier papers can require quantitative bond-energy calculations and more detailed interpretation of energy profiles and uncertainty.
Risk pitfalls and guardrails
Saying bond breaking releases energy.
Guardrail: Do not import separate-science content or another route's paper order; use the full physics equations sheet required for current specifications while checking the exact series materials and entered tier.
Treating activation energy as the total energy stored in products.
Guardrail: Do not import separate-science content or another route's paper order; use the full physics equations sheet required for current specifications while checking the exact series materials and entered tier.
Memory anchors
Exothermic reaction
A reaction transferring energy from the reacting system to surroundings.
Endothermic reaction
A reaction transferring energy from surroundings into the reacting system.
Activation energy
The minimum energy required for particles to react.
Reaction profile
A diagram showing energy change along a reaction pathway.
Mean bond energy
An average energy required to break a specified covalent bond.
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 mixture warms from 19.0 °C to 31.5 °C. What does this show?
What happens when a chemical bond is broken?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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