Why is enthalpy usually used in calculations involving the first law of thermodynamics for control volumes, while internal energy is used for closed systems?

Explanation:

In system enclosed so as to prevent the mass transfer, for such processes, at constant pressure, heat absorbed/released equals change in enthalpy.

If there is a closed system , which means that there is no exchange of heat and energy, there will be no heat absorbed/ gained. So, the enthalpy of the system is only the internal energy possessed by the system.

On the other hand, if there is change in volume at constant pressure in the system , the enthalpy is equal to the internal energy plus the product of pressure and change in volume.

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