Bond Enthalpies

[Cynthia Ulloa]

Can someone re-explain how we would use bond enthalpies? Would we only account for the new formations?

[Albert Duong 4C]

Yes, we add up the energy of each bond that is broken (since energy is required, it's a positive number because energy is going into the system of bonds) and subtract that bonds that form (energy is released from the system). The bonds that are neither broken nor formed are not factored into the calculation.

[Soumya Ravichandran 4H]

Yes, you only account for the bonds broken and re-formed. However, Dr. Lavelle mentioned in class that you can also just break down all the bonds in the reacts and re-form all the bonds in the products to get the same answer though it might be a longer process for the calculations.

[Tuong Nguyen 2I]

This method is known to be the most inaccurate one of the three however, so I don't think we'll be using this method much, other than in homework problems.