# Which of the following is not a thermodynamic state function?

A: Internal Energy

B: Work done

C: Enthalpy

D: Entropy

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**Hint:**Thermodynamic functions are those functions whose state affects the system. Thermodynamic state functions are those functions whose values don’t depend on the path taken to reach the final state of the system. These functions depend only on the initial and final state of the system.

**Complete step by step answer:**

We know state functions are those which are path independent. In this question, we have to find the function which is path-dependent which is a function that is not a state function. Internal energy is the measure of system energy which is the sum of potential energy and kinetic energy. We know energy doesn’t depend on the path; it depends on the initial and final state of the system. This means internal energy is a state function (as it is independent of the path). Enthalpy is the sum of internal energy and product of pressure and volume of the thermodynamic system. It can be calculated as:

$H = E + PV$ where $H$ is enthalpy, $E$ is internal energy, $P$ is pressure, $V$ is volume.

All these values are independent of path. So, enthalpy is also independent of path. This means enthalpy is a state function.

Entropy is defined as thermal energy per unit temperature that is available for doing work. It is also independent of the path (as energy and temperature are path independent). This means entropy is a state function. Work done is a path function (as it depends on the curve also called path) that is it is not a thermodynamic state function.

**So, the correct answer is option B that is work done.**

**Note:**

Zero Kelvin is called the absolute temperature. This is the coldest temperature possible. Absolute hot is a theoretical upper limit to the thermodynamic temperature scale, conceived as an opposite to absolute zero.