This chapter examines chemical reactions more generally than the previous chapters. In Chap. 23 the focus has been on the combustion of fossil fuels and the lower/upper heating value has been introduced to handle a chemical decomposition energetically. However, this method used to be rather impractical, since the oxidisation has to be split into several parts and a distinction has been required whether condensation occurs. Now, a more straightforward method is preferred by introducing the so-called absolute specific enthalpy/entropy. In doing so, the specific enthalpy does not only imply a caloric effect, as it has been done in part I and II, but it includes the specific chemical bonded energy as well.