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Doc Brown's Chemistry AQA GCSE Science-CHEMISTRY 2 Revision Notes

Chemistry Unit C2.5 Exothermic and endothermic reactions Study Notes

CHEMISTRY UNIT 2 Chemistry 2 for GCSE Additional Science or GCSE Chemistry

REVISION NOTES GUIDE SUMMARY: What do you need to know for the examinations? What do you need to able to do in the exams? In AQA GCSE Science A examinations HT means for higher tier students only. Sorry, but I don't have much time to answer questions, but if you see any apparent errors or wish to comment, please email me. All my notes, learning objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4 syllabus specification.

  • Throughout this unit you will be expected to write word equations for reactions specified.

  • Higher tier (HT) candidates will also be expected to write and balance symbol equations for reactions specified throughout the unit.

AQA GCSE Science CHEMISTRY Unit C2.5 Exothermic and endothermic reactions

  • Chemical reactions involve energy transfers.

  • Many chemical reactions involve the release of energy.

  • For other chemical reactions to occur, energy must be supplied.

  • You should use their skills, knowledge and understanding to evaluate everyday uses of exothermic and endothermic reactions.

    • You may be given data from which to draw conclusions.


AQA GCSE Science CHEMISTRY Unit C2.5.1 Energy transfer in chemical reactions

  • a) When chemical reactions occur, energy is transferred to or from the surroundings.

    • Knowledge of delta H (ΔH) conventions and enthalpy changes, including the use of positive values for endothermic reactions and negative values for exothermic reactions, is not required.

  • b) An exothermic reaction is one that transfers energy to the surroundings.

    • Examples of exothermic reactions include combustion, many oxidation reactions and neutralisation.

    • Everyday uses of exothermic reactions include self-heating cans (eg for coffee) and hand warmers. 

  • c) An endothermic reaction is one that takes in energy from the surroundings.

    • Endothermic reactions include thermal decompositions.

    • Some sports injury packs are based upon endothermic reactions.

  • d) If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction.

    • The same amount of energy is transferred in each case.

    • For example heating blue copper sulphate crystals:

      • hydrated copper sulfate (blue) (c) doc b anhydrous copper sulfate (white) + water

        • Right to Left <=== exothermic ===   and   === endothermic ===> Left to Right

        • (c) doc b


  • Revise demonstrations you saw or practical work you did to develop skills and understanding which may have included the following:

    • investigating temperature changes of neutralisations and displacement reactions, eg zinc and copper sulfate

    • investigating temperature changes when dissolving ammonium nitrate, or reacting citric acid and sodium hydrogencarbonate

    • adding ammonium nitrate to barium hydroxide

    • demonstration of the addition of concentrated sulfuric acid to sugar

    • demonstration of the reaction between iodine and aluminium after activation by a drop of water

    • demonstration of the screaming jelly baby

    • demonstration of the Thermite reaction, ie aluminium mixed with iron(III) oxide

    • investigation of hand warmers, self-warming cans, sports injury packs.

    • There are opportunities here for measurements using temperature sensors to investigate energy transfer.



GCSE Science-Chemistry courses AQA GCSE Science A CHEMISTRY EDEXCEL GCSE Science CHEMISTRY

OCR GCSE 21st Century Science A CHEMISTRY  *  OCR GCSE Gateway Science B CHEMISTRY

WJEC GCSE Science-CHEMISTRY  *  Northern Ireland CCEA GCSE Science-CHEMISTRY


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