2.8 Energy Changes in Chemistry
Exothermic and endothermic reactions, temperature measurements, reaction profiles, activation energy and bond-energy calculations.
How to study for CCEA GCSE Chemistry
Connect particle models to observations, balance every quantitative relationship, and prepare each prescribed practical from safe method through analysis and evaluation.
Core concepts
Concept 1
Exothermic reactions transfer energy to the surroundings while endothermic reactions take energy from them.
Exam cue: Define the system and surroundings before interpreting a temperature change.
Concept 2
Reaction profiles show reactant and product energy levels plus the activation-energy barrier.
Exam cue: Read activation energy from reactant level to profile peak.
Concept 3
Breaking bonds requires energy and making bonds releases energy, so their balance determines the overall energy change.
Exam cue: Calculate energy for bonds broken minus energy for bonds formed using correct bond counts.
Risk pitfalls and guardrails
Saying energy is released when bonds break.
Guardrail: Do not import an England board, Single Award or Double Award structure, and do not replace a particle-level explanation with a vague observation.
Equating a larger temperature change automatically with more energy without considering amounts and heat capacity.
Guardrail: Do not import an England board, Single Award or Double Award structure, and do not replace a particle-level explanation with a vague observation.
Drawing a catalyst pathway with changed reactant or product energy levels.
Guardrail: Do not import an England board, Single Award or Double Award structure, and do not replace a particle-level explanation with a vague observation.
Memory anchors
Exothermic
Transfers energy from the reacting system to the surroundings.
Endothermic
Takes energy from the surroundings into the reacting system.
Activation energy
Minimum energy barrier from reactants to a successful reaction route.
Bond breaking
Requires an input of energy.
Bond making
Releases energy.
Bond-energy change
Total energy to break bonds minus total energy released making bonds.
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
The temperature of the surroundings rises while a reaction proceeds. How is the reaction classified in terms of energy transfer?
The temperature of the surroundings falls as a reaction proceeds because energy enters the reacting system. How is this reaction classified?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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