SEC G3 Combined Science Chemistry component K326/K328
C9: Chemical Energetics
Classify exothermic and endothermic changes from energy transfer and experimental evidence.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Chemical energetics is read from the direction of energy transfer between a process and its surroundings, supported by an observed temperature change.
Exothermic transfer
An exothermic process transfers energy, often in the form of heat, to the surroundings. The surroundings commonly become warmer, as in neutralisation between sodium hydroxide and hydrochloric acid.
When the measured solution becomes warmer, that observation is evidence that energy has been transferred from the reacting chemicals to their surroundings.
Endothermic transfer
An endothermic process takes in energy, often in the form of heat, from the surroundings. The surroundings commonly cool, as when ammonium nitrate dissolves in water.
A temperature fall is evidence under controlled conditions, not the definition by itself. The definition is based on transfer direction.
Using temperature evidence
Measure an initial temperature, carry out the process, and record the greatest rise or fall while reducing energy exchange with the wider environment.
Classify only after comparing final behaviour with the initial temperature and identifying the direction of transfer.
Formulae and relationships
This chapter is assessed mainly through models, field patterns and explanations. Build the causal chain before adding any calculation.
Worked examples
Example 1: A solution cools from to as a salt dissolves. Classify the process.
- The measured surroundings became cooler.
- Energy moved from the surroundings into the dissolving process.
- A process that takes in energy is endothermic.
Answer: Endothermic.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Explain Exothermic transfer with the named terms, evidence, and causal links kept distinct.
- Use Endothermic transfer to interpret the evidence given and justify each conclusion.
- Apply Using temperature evidence to a new example, then check the conclusion against the information given.
Official outcome coverage
K326 C9: 2 mapped outcomes, references C9(a), C9(b). Check the official K326 syllabus.
K328 C9: 2 mapped outcomes, references C9(a), C9(b). Check the official K328 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Measure a temperature change in an insulated container with equal total quantities, consistent stirring and the same thermometer position. State whether the reacting system transfers energy to or takes energy from the surroundings, and explain heat exchange as a limitation.
Exam traps and retrieval check
Avoid these traps
- Defining exothermic only as hot.
- Reversing the direction of transfer.
- Ignoring heat exchange with the external environment when evaluating data.
Check from memory
Where does energy go in an exothermic process?
To the surroundings.
What commonly happens to temperature in an endothermic process?
It decreases.
What should a conclusion name besides temperature change?
The direction of energy transfer.
Official Combined Science scope
This shared Combined Chemistry owner serves both K326 and K328. Exothermic and endothermic changes described through energy transfer and observed temperature change.