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5. Chemical energetics

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  1. 5.1 Enthalpy change, ΔH

    1. 5.1.1Chemical reactions are accompanied by enthalpy

      • Understand: chemical reactions are accompanied by enthalpy changes and these changes can be exothermic (ΔH is negative) or endothermic (ΔH is positive)

    2. 5.1.2Construct/interpret a reaction pathway diagram

      • Construct/interpret: a reaction pathway diagram, in terms of the enthalpy change of the reaction and of the activation energy

    3. 5.1.3Terms

      • Define/use:: (a) standard conditions (this syllabus assumes that these are 298 K and 101 kPa) shown by ⦵; (b) enthalpy change with particular reference to: reaction, ΔHr , formation, ΔHf , combustion, ΔHc , neutralisation, ΔHneut

    4. 5.1.4Energy transfers occur during chemical

      • Understand: energy transfers occur during chemical reactions because of the breaking and making of chemical bonds

    5. 5.1.5Bond energies and ΔHr

      • Use bond energies (ΔH positive, i.e. bond breaking) to calculate enthalpy change of reaction, ΔHr

    6. 5.1.6Some bond energies are exact and some bond

      • Understand: some bond energies are exact and some bond energies are averages

    7. 5.1.7Enthalpy changes from appropriate experimental

      • Calculate enthalpy changes from appropriate experimental results, including the use of the relationships q = mcΔT and ΔH = –mcΔT/n

  2. 5.2 Hess’s law

    1. 5.2.1Hess’s law to construct simple energy cycles

      • Apply Hess’s law to construct simple energy cycles

    2. 5.2.2Calculations: cycles and relevant energy terms

      • Carry out calculations using cycles and relevant energy terms, including:: (a) determining enthalpy changes that cannot be found by direct experiment; (b) use of bond energy data