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Reaction Enthalpy & Hess’s Law Inquiry Guide & AP* Chemistry Curriculum Alignment Transition Guide


The heat or enthalpy change for a chemical reaction is called the enthalpy of reaction. This energy change is equal to the amount of heat transferred, at constant pressure, in the reaction. The enthalpy of a reaction represents the difference in enthalpy of the products and the reactants and is independent of the steps in going from reactants to products. According to Hess’s law, if a reaction can be carried out in a series of steps, the sum of the enthalpies for each step equals the enthalpy change for the overall reaction.


  • Enthalpy
  • Heat
  • Calorimetry
  • Hess's Law