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

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Engineering

Caden

31 March, 00:58

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

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Mikayla · Answer 1

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.