bond enthalpy

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  • Created by: Jasmin
  • Created on: 22-01-14 09:11
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  • Bond Enthalpy
    • Bond enthalpy is the energy
      • Required to break 1 mole of bonds
      • Released on making 1 mol of bonds
    • Energy to break bonds so bond breaking is endothermic (+)
    • Energy is released when bonds are formed, so is exothermic (-)
    • Amount of energy you need per mol is called bond dissociation enthalpy or bond enthalpy
    • Bond enthalpies influence how quickly a reaction will occur. In general the smaller the bond enthalpies of the bonds that need to be broken, the faster a reaction will be at room temp. That's because less energy has to be taken in from the surroundings to break the reactant bonds
    • Ethanol is used as a fuel. The enthalpy of combustion can be determined experimentally and also theoretically from mean bond enthalpy data.
      • Example
    • For mean bond enthalpy take an average
      • Breaking bonds is always an endothermic process so average bond dissociation enthalpies are always positive
    • Difference between calculated and experimental values arises because:
      • Calculations use average (mean) bond enthalpies
      • Bond enthalpies only apply to substances in the gaseous state
      • As in the example, it is a liquid the energy of vapourisation must be added


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