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

Chemistry Unit C2.4 Rates of reaction 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 C2.4 Rates of reaction

  • Appreciate that being able to speed up or slow down chemical reactions is important in everyday life and in industry.

  • Know that changes in temperature, concentration of solution, gas pressure, surface area of solids and the presence of catalysts all affect the rates of reactions.

    • Know that catalysts can help to reduce the cost of some industrial processes.

  • You should be able to use your skills, knowledge and understanding to:

    • interpret graphs showing the amount of product formed (or reactant used up) with time, in terms of the rate of the reaction

      • Knowledge of specific reactions other than those in the subject content for this unit is not expected, but you will be expected to have studied examples of chemical reactions and processes in developing their skills during their study of this section.

    • explain and evaluate the development, advantages and disadvantages of using catalysts in industrial processes.

      • Information may be given in examination questions so that you can make evaluations.


AQA GCSE Science CHEMISTRY Unit C2.4.1 Rates of reaction

  • a) The rate of a chemical reaction can be found by measuring the amount of a reactant used or the amount of product formed over time:

    • Rate of reaction = amount of reactant used / time

      • or

    • Rate of reaction = amount of product formed / time

  • b) Know that chemical reactions can only occur when reacting particles collide with each other and with sufficient energy.

    • The minimum amount of energy particles must have to react is called the activation energy.

  • c) Know that increasing the temperature increases the speed of the reacting particles so that they collide more frequently and more energetically.

    • This increases the rate of reaction.

  • d) Know that increasing the pressure of reacting gases increases the frequency of collisions and so increases the rate of reaction.

  • e) Know that increasing the concentration of reactants in solutions increases the frequency of collisions and so increases the rate of reaction.

  • f) Know that increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.

  • g) Know that catalysts change the rate of chemical reactions but are not used up during the reaction.

    • Know that different reactions need different catalysts.

    • Knowledge of named catalysts other than those specified in the subject content for this unit is not required, but you should be aware of some examples of chemical reactions and processes that use catalysts.

  • h) Know that catalysts are important in increasing the rates of chemical reactions used in industrial processes to reduce costs.


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

    • designing and carrying out investigations into factors such as:

      • temperature, eg magnesium with acids at different temperatures

      • surface area, eg different sizes of marble chips

      • catalysts, eg the decomposition of hydrogen peroxide using manganese(IV) oxide, potato and/ or liver; the ignition of hydrogen using platinum; oxidation of ammonia using platinum; cracking liquid paraffin using broken pot concentration, eg sodium thiosulfate solution and dilute hydrochloric acid.

    • These present opportunities for you to see/make measurements using sensors (eg carbon dioxide, oxygen, light, pH, gas pressure and temperature) to investigate reaction rates.



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