Enthalpy is the amount of energy contained in a substance. Represents a thermodynamic measurement which is represented by the letter H in capital letters, the variation of this measurement shows the amount of energy attracted or transferred by a thermodynamic system, that is, the proportion of energy that a system transfers to its environment.
The term enthalpy is derived from the Greek "enthalpos" which means to heat. Enthalpy is usually handled within the thermodynamic context to refer to the amount of energy that is in motion when a constant pressure occurs on a material object. The thermodynamic enthalpy is expressed in joule (unit of measure used in the calculation of energy, work and heat), and its formula is the following: H = U + PV.
There are three types of enthalpy:
Enthalpy of formation: represents the amount of heat that is absorbed or discharged when one mole of a compound is produced. This enthalpy will be negative, when it comes from an exothermic reaction, that is, it releases heat, while it will be positive, when it is endothermic (absorbs heat).
Enthalpy of reaction: represents the variation of enthalpies in formation, that is, the amount of heat attracted or released, in a chemical reaction when it occurs at constant pressure. The value of enthalpy will vary depending on the pressure and temperature of said chemical reaction.
Enthalpy of combustion: represents the heat discharged, at a constant pressure, at the time of burning a mole of substance. When referring to a kind of reaction where heat is released, we are talking about an exothermic reaction, so the enthalpy variation will be negative.
Standard enthalpy: it is the enthalpy variation that originates within a system when a similar unit of matter is altered through a chemical reaction under normal conditions.
Solidification enthalpy: refers to the amount of energy that is convenient to release, so that a mole of substance, with constant temperature and pressure, moves from a solid state to a liquid state.
Enthalpy of vaporization: it is the one where energy must be consumed to be able to vaporize a mole of substance, that is, to go from a liquid to a gaseous state. As the attracted energy is in the form of heat, it is facing an endothermic process, therefore, the change in enthalpy will be positive.
