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Exothermic and endothermic reactions
This topic connects energy conservation to heating and cooling effects, then uses reaction profiles and bond energies to describe why reactions are exothermic or endothermic.
36
Objectives
190
Flashcards
190
Questions
90 min
Study time
AQAGCSEChemistryEnergy changes
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Syllabus checklist
What you need to know
36 objective pages available
Energy transfer during exothermic and endothermic reactions14 objectives
- State that energy is conserved in chemical reactions.
- Explain that a reaction transferring energy to the surroundings leaves products with less energy than the reactants by the amount transferred.
- Define an exothermic reaction as one that transfers energy to the surroundings.
- Explain that the temperature of the surroundings increases during an exothermic reaction.
- Identify combustion, many oxidation reactions and neutralisation as examples of exothermic reactions.
- Describe everyday uses of exothermic reactions, including self-heating cans and hand warmers.
- Define an endothermic reaction as one that takes in energy from the surroundings.
- Explain that the temperature of the surroundings decreases during an endothermic reaction.
- Describe sports injury packs as an everyday use of endothermic reactions.
- Distinguish between exothermic and endothermic reactions using the temperature change of the surroundings.
- Evaluate uses and applications of exothermic and endothermic reactions from given information.
- Describe how to measure temperature changes when substances react or dissolve in water. (AT 5)
- Describe the required practical to investigate variables that affect temperature changes in reacting solutions such as acid plus metal, acid plus carbonate, neutralisation and displacement reactions. (AT 1, AT 3, AT 5, AT 6)
- Explain why calculation of enthalpy change or ΔH is not required for this GCSE section.
Reaction profiles10 objectives
- Explain that chemical reactions occur only when reacting particles collide.
- Explain that reacting particles must collide with sufficient energy for a reaction to occur.
- Define activation energy as the minimum energy particles need to react.
- Draw a simple reaction profile for an endothermic reaction.
- Label reactants and products on a reaction profile.
- Label activation energy on a reaction profile.
- Label the overall energy change on a reaction profile.
- Use reaction profiles to identify whether a reaction is exothermic or endothermic.
- Explain that the curved line on a reaction profile shows how energy changes as the reaction proceeds.
- Compare the relative energies of reactants and products in exothermic and endothermic reaction profiles.
The energy change of reactions (HT only)12 objectives
- (HT only) State that energy must be supplied to break bonds in reactants.
- (HT only) State that energy is released when bonds in products are formed.
- (HT only) Explain that bond energies can be used to calculate energy needed to break bonds.
- (HT only) Explain that bond energies can be used to calculate energy released when bonds form.
- (HT only) Calculate the total energy needed to break bonds in reactants from supplied bond energies. (MS 1a)
- (HT only) Calculate the total energy released when bonds form in products from supplied bond energies. (MS 1a)
- (HT only) Calculate the overall energy change as energy needed to break bonds minus energy released when bonds form.
- (HT only) Explain why a reaction is exothermic when energy released from forming bonds is greater than energy needed to break bonds.
- (HT only) Explain why a reaction is endothermic when energy needed to break bonds is greater than energy released from forming bonds.
- (HT only) Use supplied bond energy data to calculate the energy transferred in a chemical reaction.
- (HT only) Include the correct sign or direction of energy transfer when interpreting a calculated energy change.
- (HT only) Distinguish bond energy calculations from reaction profile interpretation.
Key terms
Energy conservationChemical reactionExothermic reactionEndothermic reactionSurroundingsCombustionSelf‑heating canHand warmerThermal decompositionSports injury packTemperature changeReactants
Exam tips
- Understand Energy Conservation: Explain always remember that energy is conserved in chemical reactions; it cannot be created or destroyed. Link your answer to Energy transfer during exothermic and endothermic reactions in Exothermic and endothermic reactions; for bond-energy work, separate bonds broken from bonds formed and include the sign and unit.
- Understand Energy Transfer: Focus on how energy is transferred during reactions and how it affects the energy of products compared to reactants.
Common mistakes
- Misunderstanding Energy Conservation: Emphasize that energy is conserved in chemical reactions; it can change forms but is never lost.
- Confusing Energy Transfer: Remember that in an exothermic reaction, energy is transferred to the surroundings, resulting in products that have less energy than the reactants.
Practice preview
- For Energy transfer during exothermic and endothermic reactions, which answer best supports this AQA GCSE Chemistry Unit 4.5 objective: State that energy is conserved in chemical reactions?
- Which statement gives the clearest definition of state in Energy transfer during exothermic and endothermic reactions?
- Which exam-check sentence would most directly answer a question about state?
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