Does the absolute value of enthalpy have any physical significance?

Question

I know it is pretty hard to measure the change in volume in open systems. Accordingly, calculating the change in internal energy using the first law of thermodynamics is pretty hard also. Is this the only reason for introducing enthalpy ($H$) as a new thermodynamic potential to make use of the constant atmospheric pressure, and to calculate the change in enthalpy ($\Delta{H}$) as it is equal to the in/out quantity of heat ($Q$) in this case?

If no, does the absolute value of enthalpy have any physical significance?

Answer 1

If you are familiar with the open system (control volume) version of the 1st law of thermodynamics, then you know that, for process streams passing through continuous flow equipment operating at steady state (like chemical plants, power plants, ventilation systems, air conditioners, heaters, etc), the important parameter to follow is the enthalpy of the streams, not their internal energy. This includes distillation columns, absorption columns, chemical reactors, flash separators, ion exchangers, heat exchangers, turbines, condensers, etc.

In vapor-liquid equilibrium behavior and chemical reaction equilibrium behavior, the temperature dependence of the vapor pressure or the chemical equilibrium constant is expressed most simply in terms of the standard enthalpy change for the reaction.