3.2.1
Enthalpy Changes
Section 3.2.1 covers enthalpy changes: exothermic and endothermic reactions, enthalpy profile diagrams and activation energy, standard conditions and standard states, the enthalpy changes of reaction, formation, combustion and neutralisation, determining enthalpy changes from q = mcΔT, average bond enthalpies, and Hess’ law cycles using combustion, formation and unfamiliar data.
Revision Notes
5 revision notes, in the order the specification teaches them.
Enthalpy Changes and Standard Conditions
Exothermic and endothermic reactions, enthalpy profile diagrams, activation energy and standard conditions.
Start revising
Standard Enthalpy Changes
The standard enthalpy change definitions and the equation each one refers to.
Start revising
Calorimetry: Measuring Enthalpy Changes
Calculating ΔH from a temperature change, cooling curve corrections, errors and assumptions.
Start revising
Hess’s Law and Enthalpy Cycles
Building enthalpy cycles and calculating ΔH from formation and combustion data.
Start revising
Bond Enthalpies
Average bond enthalpy, calculating ΔH from bonds broken and made, and why the answers differ from Hess values.
Start revisingSummary Map
Download, print and revise the key facts of this topic at a glance.
Summary maps
Download, print and revise the key facts of this topic at a glance.
Enthalpy Profiles and Definitions Map
OCR A Level Chemistry A · 3.2.1 Enthalpy changes: Enthalpy profiles and definitions
The whole section on one A4 page: ΔH and its sign, enthalpy profiles and Eₐ, standard conditions and the standard enthalpy changes.
Calorimetry Map
OCR A Level Chemistry A · 3.2.1 Enthalpy changes: Calorimetry
The whole section on one A4 page: q = mcΔT, reactions in solution, burning fuels, errors and assumptions, uncertainty and the cooling-curve correction.
Hess's Law Map
OCR A Level Chemistry A · 3.2.1 Enthalpy changes: Hess's law
The whole section on one A4 page: Hess's law, formation and combustion cycles, combining equations, PAG 3 and evaluating the result.
Bond Enthalpies Map
OCR A Level Chemistry A · 3.2.1 Enthalpy changes: Bond enthalpies
The whole section on one A4 page: bond enthalpy, average bond enthalpy, ΔH from bonds broken and made, working back, limitations and which bond breaks first.
© 2026 Online Learning System. For personal study: printing is allowed; editing, copying and redistribution are not.
Virtual Lessons
Recorded video lessons that teach the topic step by step.
The Virtual Lessons for 3.2.1 Enthalpy Changes are being recorded.
MCQ Bank
Multiple-choice papers on this topic, marked the moment you submit.
The MCQ papers for 3.2.1 Enthalpy Changes are being written.
SAQ Bank
Written, drawn and worked exam practice on this topic.
The exam practice papers for 3.2.1 Enthalpy Changes are being written.
Revision Game
Match reagents to products, with your board's reagents and conditions.
The revision game for 3.2.1 Enthalpy Changes is being built.
Study Cards
Pick a deck, then turn each card to check what you remember.
Specification
Every specification point in this topic, in the exam board's own words. Rate how confident you are with each one.
Self-assessment · 20 points
Sign in to rate how confident you feel about each point. Your ratings are saved to your account, follow you to any device, and appear beside your KASP analytics, kept apart from your marks.
3.2.1
- a i
explanation that some chemical reactions are accompanied by enthalpy changes that are exothermic (ΔH, negative)
Revise - a ii
explanation that some chemical reactions are accompanied by enthalpy changes that are endothermic (ΔH, positive)
Revise - b
construction of enthalpy profile diagrams to show the difference in the enthalpy of reactants compared with products
Revise - c
qualitative explanation of the term activation energy, including use of enthalpy profile diagrams
Revise - d (i) b
explanation and use of the term standard states (physical states under standard conditions)
Revise - d (ii)
explanation and use of the term enthalpy change of reaction (enthalpy change associated with a stated equation, ΔrH)
Revise - d (iii)
explanation and use of the term enthalpy change of formation (formation of 1 mol of a compound from its elements, ΔfH)
Revise - d (iv)
explanation and use of the term enthalpy change of combustion (complete combustion of 1 mol of a substance, ΔcH)
Revise - d (v)
explanation and use of the term enthalpy change of neutralisation (formation of 1 mol of water from neutralisation, ΔneutH)
Revise - e
determination of enthalpy changes directly from appropriate experimental results, including use of the relationship: q = mcΔT
Revise - f (i)
explanation of the term average bond enthalpy (as the breaking of 1 mol of bonds in gaseous molecules)
Revise - f (ii) a
explanation of exothermic reactions in terms of enthalpy changes associated with the breaking and making of chemical bonds
Revise - f (ii) b
explanation of endothermic reactions in terms of enthalpy changes associated with the breaking and making of chemical bonds
Revise - f (iii)
use of average bond enthalpies to calculate enthalpy changes and related quantities (see also 2.2.2 f)
Revise - g (i)
Hess' law for construction of enthalpy cycles and calculations to determine indirectly an enthalpy change of reaction from enthalpy changes of combustion
Revise - g (ii)
Hess' law for construction of enthalpy cycles and calculations to determine indirectly an enthalpy change of reaction from enthalpy changes of formation
Revise - g (iii)
Hess' law for construction of enthalpy cycles and calculations to determine indirectly enthalpy changes from unfamiliar enthalpy cycles
Revise
Keep this note — free
Save your progress across every OCR topic. A free account remembers which topics you have covered, saves your question scores, and syncs across your phone and laptop.
- Track every topic you have finished
- Keep your practice-question scores
- No payment, no card, free forever
Already registered? Log in