3.2.1 Bond Enthalpy

Question 1

define average bond enthalpy

Answer 1

average bond enthalpy is the average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species

Question 2

what is always required to break bonds

Answer 2

Energy is always required to break bonds, therefore bond enthalpies are always endothermic and have positive enthalpy values.

Question 3

how is average bond enthalpy calculated

Answer 3

it is calculated from the actual bond enthalpies in different chemical enviroments

Question 4

how do you calculate 𝚫H from average bond enthalpies

Answer 4

𝚫Hr = 𝚺(bond enthalpies in reactants) - 𝚺(bond enthalpies in products)

𝚺 = sum of

Question 5

when are bonds endothermic and exothermic

Answer 5

Breaking bonds is endothermic (energy is needed and taken in from the surroundings)
Making bonds is exothermic (energy is released to the surroundings)

Question 6

what is 𝚫H

Answer 6

𝚫H is the difference between the energy used to break bonds and the energy released making bonds

Question 7

What is a limitation of using average bond enthalpies in calculations

Answer 7

The actual energy involved in breaking and making bonds would be slightly different. Despite this the calculated enthalpy change of reaction should be in general agreement with the actual enthalpy change of reaction.