In thermodynamics, the enthalpy of a system is defined as the sum of the internal energy of the system and the product of its pressure and volume. Since it is just a combination of other state properties of the system, why need we define it at all?

Aliyah Thompson

Aliyah Thompson

Answered question

2022-11-16

In thermodynamics, the enthalpy of a system is defined as the sum of the internal energy of the system and the product of its pressure and volume. Since it is just a combination of other state properties of the system, why need we define it at all?

Answer & Explanation

mainzollbtt

mainzollbtt

Beginner2022-11-17Added 13 answers

We define everything in physics because it's useful. In this case it's useful when a fluid flows in a steady state system and you want to look at energy flows. If a fluid flows through a box, and has a change in specific enthalpy h, with a flow rate of m ˙ , then the power transferred to the fluid is m ˙ h
Sometimes all you know is the energy change, which can tell you the change in enthalpy, but without more information, you don't know how much is heat and how much is pressure. So by using enthalpy you can simplify the problem.

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