9.3 Bond Enthalpies

Question 1

What is average bond enthalpy?

Answer 1

Energy required to break one mole of a specified type of bond in a gaseous molecule

Question 2

Are bond enthalpies endothermic or exothermic?

Answer 2

Endothermic, take in energy from surroundings

Question 3

Limitations of actual bond enthalpy

Answer 3

Average bond enthalpy is calculated from actual bond enthalpies in different environments

Question 4

Exothermic reactions

Answer 4

Energy released from bond formation > energy absorbed for bond breaking

Question 5

Endothermic reactions

Answer 5

Energy released from bond formation < energy absorbed for bond breaking

Question 6

Calculating enthalpy change of reaction

Answer 6

Bond enthalpy of reactants - bond enthalpy of products

Question 7

Hess’ Law

Answer 7

If a reaction can take place by two routes, and the starting and finishing conditions are the same, the total enthalpy change is the same for each route