Topic 8 definitions

Question 1

standard enthalpy change, H ⦵

Answer 1

The heat energy change at constant pressure under standard conditions (pressure 100
kPa ; temperature 298 K

Question 2

Standard molar enthalpy change of formation, H f ⦵

Answer 2

The enthalpy change when one mole of a compound is formed from its constituent
elements under standard conditions, with all reactants and products in their standard states.

Question 3

Standard molar enthalpy change of combustion, H c ⦵

Answer 3

The enthalpy change when one mole of a compound is completely burned in excess
oxygen under standard conditions, all reactants and products in their standard states.

Question 4

Mean bond energy

Answer 4

The enthalpy change when 1 mole of a particular type of bond is broken or made (all
species in the gas phase) averaged over many different molecules