Abstract The key and difficult points of physical chemistry may be the calculation of reaction enthalpy. Reaction enthalpy, formation enthalpy and combustion enthalpy often make the beginners confused in the calculation process. By designing energy level diagrams, including reaction enthalpy, formation enthalpy, combustion enthalpy and so on, it was discovered that those diagrams were helpful to simplify the calculation process and to clearly make a distinction about different enthalpies above-mentioned.
