Question

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

Answer 1

Hint: To answer this question, we should know about state function. We should know that state functions depend only on the state of the system, not on the path used to get to that state.

Complete step by step answer:

In this question we have to answer about that option which is not a state function. To answer that, we should note that a state function is a property whose value does not depend on the path taken to reach that specific function or value. Let us consider this by taking one example: whether we take tap water, well water or water from a bottle, all have the same density. Because, density is a state function.
In the same way, we will take each example and then we will determine the option which is not a state function.

1. Internal energy: We should know that internal energy does not depend on the path used to go from initial state to final state. It depends only on the state of the system. Hence, internal energy is called state function.
2. Entropy: We should note that entropy is a state function. The entropy change is determined by its initial and final states only.
3. Work: We should note that work is a path function. We know that a state function is one which doesn't depend on the path; the system has gone through during the process, but as
   Work done= force × displacement
   And displacement is a path function. So, work is also a path function
4. Enthalpy: We should consider enthalpy a state function because its current value will only depend upon the final and initial values of heat in a reaction, but not the path or process that occurred for it to reach that value.
   So, from the above discussion, we can now say that from the options given in question, we can now say that work is not a state function. Work is a path function. Our correct option is C.

Note:The important point that we should remember when trying to identify a state function is to determine whether the path taken to reach the function affects the value. Let us take an example, if we want to get to the fourth floor of the building. Going from ground floor to fourth floor is a change in our vertical position. Whether we take the stairs, elevator or escalator we arrive at the same fourth floor. This change in vertical position is state function. But the amount of time in each ride is different. It will be maximum by going with stairs than in escalator and lift.