CHAPTER 6: Chemical Energetics

• Enthalpy Changes
• Standard Enthalpy Changes
• Hess’ Law
• Bond Energy

Learning outcomes:

• explain that some chemical reactions are accompanied by energy changes, principally in the form of heat energy; the energy changes can be exothermic (∆H, negative) or endothermic.
• explain and use the terms:
  • enthalpy change of reaction and standard conditions, with particular reference to: formation, combustion, hydration, solution, neutralisation, atomisation
  • bond energy (∆H positive, e. bond breaking).
• calculate enthalpy changes from appropriate experimental results, including the use of the relationship enthalpy change, ∆H = –mc∆
• apply Hess’ Law to construct simple energy cycles, and carry out calculations involving such cycles and relevant energy terms, with particular reference to:
  • determining enthalpy changes that cannot be found by direct experiment, g. an enthalpy change of formation from enthalpy changes of combustion.
  • average bond energies
• construct and interpret a reaction pathway diagram, in terms of the enthalpy change of the reaction and of the activation energy