Definitions

• What is the definition of enthalpy change (ΔH)?

  Heat energy change measured at constant pressure
• What is the First Law of Thermodynamics?

  Energy cannot be created or destroyed
• What is the standard enthalpy change of formation (ΔHf)?

  Enthalpy change when one mole of substance forms from elements under standard conditions and with all substances in their standard states
• What is the standard enthalpy change of combustion (ΔHc)?

  Enthalpy change when one mole of substance burns in oxygen under standard conditions with all SUBSTANCES in their standard states
• What’s the mean bond enthalpy

  • Enthalpy change at constant pressure needed to break covalent bonds
  • AVERAGED FOR THAT TYPE OF BOND over a range of different compounds
• Define Hess’s law

  The enthalpy change at constant pressure in a reaction is independent of the path taken

  AND depends only on the initial and final states