Termoquímica: validez de la definición del cambio de entalpía aplicado a una reacción química

In this communication we have examined the validity of the definition of enthalpy change of a chemical reaction. In the first place, we have discussed fundamental concepts such as the first and the second laws of thermodynamics in order to understand some derivations from them. Next, we analyzed the application of these concepts to chemical reactions that take place at constant pressure. From this analysis, it can be concluded that the characteristics of the reaction being investigated in a thermochemical experiment are of paramount importance for interpreting the heat of the measured reaction. Hence, it should be taken into account the possibility of useful work exchange among the system and the surroundings in addition to the reaction heat at constant pressure.