BRAINCAKE

Energetics

AQA AS-level ChemistryTopic 4 of 1324 lessons

Revision notes for Energetics in AQA Chemistry (7404). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.

  1. Endothermic and Exothermic ReactionsThe law of conservation of energy states that energy cannot be created or destroyed.
  2. Enthalpy Change ΔHEnthalpy is a measure of the total energy of a chemical system.
  3. Physical States of Reactants and ProductsReactants and products can be solids, liquids or gases.
  4. Enthalpy Level DiagramsEnthalpy level diagrams represent enthalpy changes and show the relative levels of energy of the reactants and products.
  5. Standard EnthalpiesEnthalpy changes are measured on a set of standard conditions as the enthalpy changes can vary with temperature, pressure or concentration.
  6. Measuring the Enthalpy Change of A ReactionTo determine the enthalpy change of the reaction the heat given out or taken in as the reaction proceeds is calculated by using the specific heat…
  7. Simple ColorimeterA known volume e.g.
  8. Flame ColorimeterA flame calorimeter is an improved apparatus for measuring enthalpies of combustion.
  9. Neutralisation ReactionsNeutralisation reactions occur when an acid reacts with a base to form a salt and water.
  10. Displacement ReactionsZinc is more reactive than copper so zinc will displace copper from copper sulfate.
  11. Allowing for Heat LossCooling curves correct for heat loss to the surroundings.
  12. Hess's Law and Thermochemical CyclesIf a reaction can take place by two routes the total enthalpy change for each route is the same provided that the starting and finishing conditions…
  13. The Enthalpy Change of FormationThe standard enthalpy of formation, ΔfH is the enthalpy change when one mole of compound is formed from its constituent elements in their standard…
  14. The Enthalpy Change of CombustionThe standard enthalpy change of combustion is defined as: The enthalpy change when one mole of a substance in its standard state burns completely in…
  15. Thermochemical Cycles and Enthalpy DiagramsHess's law states that the enthalpy change for a reaction is independent of the route taken, provided the initial and final conditions are the same.
  16. Bond EnthalpiesThe average bond enthalpy is the energy required to break one mole of a specified type of bond in a gaseous molecule.
  17. Using Mean Bond Enthalpies to Calculate Enthalpy ChangeThe enthalpy change is calculated from total bond enthalpies reactants - total bond enthalpies products. bond mean bond enthalpy kJmol-1 N≡N 945 H-H…
  18. Comparison with Thermochemical CyclesThere are limitations to using mean bond enthalpies to calculate enthalpy changes.
  19. Example Question - 1When 0.460 g of ethanol, C2H5OH, was burnt in a spirit burner, the temperature of 100 g of water in a copper can rose by 14.0 K.
  20. Example Question - 250.0 cm3 of 1.00 mol dm-3 hydrochloric acid was mixed with 50.0 cm3 of 1.00 mol dm-3 sodium hydroxide in a polystyrene cup.
  21. Example Question - 3Use the standard enthalpies of formation below to calculate the enthalpy change of combustion of propane.
  22. Example Question - 4The enthalpy of formation of ethanol cannot be measured directly, because carbon, hydrogen and oxygen do not react together to form ethanol.
  23. Example Question - 5Use the mean bond enthalpies below to calculate the enthalpy change for the combustion of methane.
  24. Example Question - 6Hydrogen and chlorine react as shown.

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