Bond Dissociation Energies:

Bond dissociation energies are a quick and powerful tool to get at least a fair estimate of the DH of a reaction. There are two major limitations to these:

Bond energies listed can only be averages. For instance, the B. E. of a C-H bond where the C is bonded to another C won't necessarily be quite the same as if the C were bonded to an N or to an O. What you have to hope for is that your errors cancel out!
Bond energies apply only to the enthalpy changes of reactions where both reactants and products are in the gas phase. If solids or liquids enter in, you must add or subtract the appropriate heats of fusion, vaporization or sublimation.

These may seem like severe limitations, but there is still a lot which can be done with these!

Problem 8.74: Use the bond dissociation energies in Table 7.1 to calculate an approximate DH° (in kJ) for the reaction of ethylene with hydrogen to yield ethane.

The general formula is (and we shall write it the right way and eschew the wimpy way it is done in the book) as follows:

That is, we sum all the bonds in reactants and subtract the same sum formed with the product bonds. (The ordering is different than that for heats of formation because dissociation energies are entered as positive numbers. That is, these are energies for the breaking of bonds; energies for forming the bonds are opposite in sign, of course!
This is then just a matter of doing some plugging in of numbers along with some simplifications in some cases. We show this now with this example.
First, here is the needed table from the text.

For the reaction in this problem, the calculation is now done.

We did an algebraic simplification followed by the actual calculation. This is a little bit different than how the book does things--and better.

Problem 8.77: Use the bond dissociation energies in Table 7.1 to calculate an approximate heat of reaction, DH° (in kJ), for the industrial reaction of ethanol with acetic acid to yield ethyl acetate (used as nail-polish remover) and water.

This is much like the previous problem--but a little more complicated. Here is the solution. The mathematically literate will find this a breeze and those who can't balance their checkbooks even will be in abject misery.

This is literally "Much Ado About Nothing"! For reference, here is the relevant table again:

As you can see, there is very little bond energy change in the formation of esters. Here, the gas phase information does not tell the whole story! You need extra information from the solution phase as described in the short summary at the start of this section.