Question

Which of the following is not a state function?
(A) Internal energy
(B) Enthalpy
(C) Work
(D) Entropy

Answer 1

The properties whose value depends upon path does not come under state function i.e. they are considered as path function or process function. State functions are dependent upon the state of the system i.e. temperature, volume, pressure, etc. of the system.

Complete step by step solution:
The thermodynamic properties which depend only on initial and final states of the system and not on how the change is brought about are called the state functions. A state function is also referred to as “point function”. These functions are the functions whose values depend on the state of the substance like temperature, pressure or the amount or type of the substance. In short, state functions do not depend on how the state was reached.
Whereas, those properties which depend on the path from two points are known as path functions, also called “process function”.
Looking at the options given,
-Internal energy: refers to the sum of all kinds of energy associated with molecular motion. The internal energy of real gases is a function of temperature, pressure and volume whereas, of ideal gases is a function of temperature only. So, it can be seen that internal energy is a state function.
-Enthalpy: refers to the sum of the system’s internal energy and the product of its pressure and volume. Thus, it depends on the state function i.e. pressure and volume.
-Work: is equal to the amount of force multiplied by the distance covered by the system. Thus, it can be seen that it depends on the distance which is not a state function. So, work is not a state function rather it is a path function.
-Entropy: is the measure of imbalance in the system and it is independent of the path. So, it is a state function.

Hence, the correct option is C.

Note: State functions also called as point functions are referred to as the functions which are dependent on the properties of the system only i.e., they are independent of the process which the system undergoes. So, it should be kept in mind which properties are dependent on which functions and it will be easy to decide whether that property is a state function or a path function.