Energetics

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  • Created by: Shannon
  • Created on: 05-03-14 09:12
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  • Energetics
    • Enthalpy changes
      • Endothermic
        • Heat energy is taken in
        • The energy required to break the bonds in the reactants is greater than the energy released when new bonds are formed.
        • ?H is +ve
      • Exothermic
        • Heat energy is released
        • The energy released by bond formation in the products is greater than the energy needed to break the bonds in the reactants.
        • ?H is -ve
      • Presented in energy level diagrams
    • Calorimetry
      • Heat capacity
        • The amount of energy needed to raise the temperature of an object by 1K
        • Measured in joules
        • Energy transferred = mc?T
      • Sources of error
        • Incomplete combutstion
        • Heat loss to surroundings
        • Heat capacity of calorimeter
    • Standard enthalpy change of combustion
      • The enthalpy change when one mole of substance is completely burnt in oxygen under standard conditions
    • Standard enthalpy change of atomisation
      • The enthalpy change when one mole of gaseous atoms is formed from its element under standard conditions
    • Standard enthalpy change of formation
      • The enthalpy change when one mole of compound is formed from its elements under standard conditions
    • Hess' law
      • The total energy change for a reaction is independent of the route taken
    • Standard enthalpy of neutralisation
      • The enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water
    • Terms
      • Bond dissociation enthalpy
        • The energy needed to break one mole of bond to give separated atoms (gaseous state)
  • Enthalpy changes
    • Endothermic
      • Heat energy is taken in
      • The energy required to break the bonds in the reactants is greater than the energy released when new bonds are formed.
      • ?H is +ve
    • Exothermic
      • Heat energy is released
      • The energy released by bond formation in the products is greater than the energy needed to break the bonds in the reactants.
      • ?H is -ve
    • Presented in energy level diagrams

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