Highest Bond dissociation energy?

Can somebody explain in detail the difference between bond energy and bond-dissociation energy?

• Answer:

  Bond dissociation energy is the enthalpy change per mole or per bond, when a bond is split by homolytic fission at a temperature of absolute zero. In homolytic fission a bond is split so that each half retains half of the electrons involved in the bond - so that two free radicals are formed. An example would be splitting methane by pulling away one hydrogen atom with its unpaired electron, leaving a methyl radical with one unpaired electron - you form two reactive groups this way. Bond energy is quite a bit different - it is related to the enthalpy change required to split a molecule completely into its constituent atoms. So in methane there are 4 carbon hydrogen bonds, you break them all up, and that requires a certain input of heat per mole - the result is 4 moles of hydrogen and one mole of carbon. The bond energy of the carbon hydrogen bond in methane will be that enthalpy change divided by 4. Bond energy can be used to estimate enthalpy of formation of molecules to within a few percent, just given tables of bond energies and counting up the number and type of bonds in a given molecule. So bond dissociation energy is a lot more specific - it will be different depending on the molecule and the particular bond that is split. If you continue to split off hydrogen atoms from the methyl radical formed in the first example - the bond dissociation energies will be different for each hydrogen.