module 3: 9.3 bond enthalpies

Question 1

define the term average bond enthalpy

Answer 1

average bond enthalpy is the energy required to break one mole of a specified type of bond in a gaseous molecule

• energy is always required to break bonds
• bond enthalpies are always endothermic
• bond enthalpies always have a positive enthalpy value

Question 2

is bond-breaking endothermic or exothermic

Answer 2

energy is required to break bonds, bond-breaking is ENDOTHERMIC (∆H is positive)

Question 3

is bond-making endothermic or exothermic

Answer 3

energy is released when bonds form, bond making is EXOTHERMIC (∆H is negative)