# In enthalpy, is PV the pressure energy?

In the case of a fluid, does the $PV$ contribution to the enthalpy correspond to the pressure energy in fluid mechanics? (Related: What is Pressure Energy?)

• Please define the term "pressure energy in fluid mechanics." – Chet Miller Mar 21 '16 at 19:11
• the energy stored in a fluid that is under pressure and has thus the potential to produce work – ergon Mar 21 '16 at 20:13
• OK. It is easy to string words together like this, but hard to provide a precise description of the concept. Let me ask it in another way. What is the mathematical definition of pressure energy? Please provide a specific example for how PV represents energy stored in a fluid, and how it does work. – Chet Miller Mar 21 '16 at 23:40
• dPdV is the work done when there is no change in temperature – ergon Mar 22 '16 at 20:17
• How can that be possible? This is the product of two differentials, so it must be taken as zero. In a closed system, irrespecitve of whether the temperature is constant, the work done by the system on the surroundings is always equal to the integral of $P_{ext}dV$, where $P_{ext}$ is the pressure at the interface between the system and the surroundings. Hasn't this been covered in your thermodynamics course? – Chet Miller Mar 22 '16 at 20:26