Steve Marsden’s

Bond energies are limited in their application for the reasons discussed earlier. They were:

  • values are for gases only
  • many values are averages

These are serious drawbacks if you want energy information about most reactions. Fortunately there is another way.

Remember in our definition of enthalpy (H) we said it was a "state function". The net enthalpy change (DH--which is the only kind of enthalpy quantity we can measure) is independent of path. What does this mean?

If a process can be carried out in a single step, the enthalpy change for that step will be the same as for a series of steps which add up to give the same overall step.