Chapter 4

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  • Chapter 4 Summary
    • Hess's Law
      • The chemical change for a chemical reaction is the same whatever route is taken
    • Flame Calorimeter
      • Improved version of simple calorimeters used for measuring enthalpy changes of combustion
      • Following features reduce heat loss futher: fuel burns in pure oxygen rather than air
    • Example of a Formation
    • Example of Combustion
    • Bond enthalpy
      • Bond dissosciation enthalpy: defined as the enthalpy change required to break a covalent bond with all species in gaseous state
      • Mean bond enthalpy: same  bond may have slightly different bond enthalpies in different molecules
    • Thermochemistry
      • when chemical reactions take place chemical bonds break and new bonds form
      • Energy given out in a reaction is exothermic
      • Energy taken in a reaction is endothermic
    • Enthalpy change
      • When you measure a heat change at a constant pressure
      • Standard conditions for measuring enthalpy change are: pressure of 100kPa and temperature of 298k
    • Exothermic and Endothermic reactions
      • Neutralising an acid with an alkali = Exothermic reaction
      • Break down of limestone to lime and carbon dioxide = Endothermic reaction
    • Standard Enthalpies
      • Standard molar enthalpy of formation
        • The enthalpy change when 1 mole of a substance is formed from its elements in standard states under standard conditions
      • Standard molar enthalpy of combustion
        • The  enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions
    • Enthalpy level diagrams
    • Measuring the enthalpy change of a reaction.. 3 things need to know
      • Mass of the substance that is being heated
      • Temperature change
      • Specific heat capacity of a substance

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