9.3 - Bond Enthalpies Flashcards
1
Q
Define average bond enthalpy
A
Average enthalpy change that takes place when breaking (by homolytic fission) one mole of a given type of bond in the gas state.
2
Q
What are the characteristics of average bond enthalpies?
A
- Energy is always required to break bonds
- Bond enthalpy is always endothermic
- Bond enthalpy always has +ve delta H
3
Q
What are the limitations of average bond enthalpy?
A
- Actual bond enthalpy relies on chemical environment
whereas aveage bond enthalpy averages actual bond enthalpies
4
Q
Bond breaking and making, exo- or endo- thermic?
A
Breaking - Endo
Making - Exo
5
Q
For a reaction involving gaseous molecules of covalent substances when calculating energy change from average bond enthalpies..
A
Enthalpy change of reaction =
Sum of bond enthalpies in reactants - sum of bond enthalpies in products
