A2

Question 1

give 2 reasons why enthalpy changes calculated from average bond enthalpies are not standard enthalpy changes

Answer 1

actual bond enthalpies for bonds broken and bonds made may be different than average bond enthalpies

alcohols and water are liquids under standard conditions. bond enthalpies apply to gases

Question 2

state what is meant by the term average bond enthalpy. explain why you would expect the actual C=O bond enthalpy to be different in CO2 and H2C=O

Answer 2

the energy needed to break one mole of a specific type of bond in a gaseous molecule
the bonds are in different environments.