Energetics: Hess's Law

Energetics: Hess’s Law

• Hess’s Law notes total enthalpy change is independent of route.
• The law is used to deduce unknown enthalpy change from known enthalpy changes.
• Bond enthalpies describe heat energy needed to break a mole of bonds in gaseous phase.
• Practice involves calculating enthalpy changes for reactions, using enthalpies of formation and combustion.
• Correct signs (+/-) of enthalpy changes are crucial for accurate calculations.