Enthalpy is a concept linked to thermodynamics that serves to name the amount of energy that each substance contains. There is no way to determine the enthalpy value of any substance, usually working with the concept of enthalpy variation in reactions and changes in physical state . The value of this exchange is due to the difference between the enthalpy of the products and the reagents.
Just as there are different types of chemical reactions and physical state changes, there are also different types of enthalpy. From this we can differentiate the following:
of change of physical state: as its name says, it refers to the amount of energy needed for a mole of substance, constant pressure and temperature to change physical state. Within this type of enthalpy there are several subtypes:
Vaporization: energy that needs to be consumed to vaporize (go from a liquid to a gaseous state) one mole of a substance. As the absorbed energy is in the form of heat, it is an endothermic process and the enthalpy value will always be positive.
of fusion: energy needed to make one mole of substance pass from solid to liquid. In this case, as in the previous one, it is an endothermic process, as the enthalpy will have a positive value in all cases.
of combustion: energy released during the complete combustion of one mole of substance at constant pressure and temperature. This type of reaction that releases energy in the form of heat is an exothermic reaction and the enthalpy change becomes negative.
of solidification: the amount of energy that needs to be released for one mole of substance, constant temperature, and pressure to change from liquid to solid. This is also an exothermic process and the enthalpy value is negative.
of formation: is the heat released or absorbed in the formation of one mole of substance from its corresponding elements, which are simple substances, with constant pressure and temperature and with an enthalpy equal to zero.
Dissolutionn: it is the sum of the reticular enthalpy (absorbs energy) and the hydration enthalpy (releases energy). Occurs when a solution dissolves in water producing a dissolution. If the variation value of this dissolution is negative, then the process is exothermic; if the value is positive, then it is an endothermic dissolution.