Question

Which of the following is not a state function?
A.) Work-done in adiabatic process
B.) Work-done in isothermal process
C.) Heat at constant pressure
D.) Heat at constant volume

Answer 1

Hint: The property whose value does not depend on the path is called a state function. Use this concept and answer the question.

Step By Step Answer:

We have to state which of the following among the given options is not a state function.
As, we know the property or a function which does not depend on the path is called a state function.

So, to know which one is a state function or not, let us study about each of the following options-

Work done in adiabatic process-

Work-done in adiabatic processes is equal to the negative of change in internal energy from the first law of thermodynamics. So, it is a state function.

Work-done in isothermal process-

For work-done in isothermal process, we can write-
$dQ = dW$

The above process is path dependent.
Heat at constant pressure-

For heat at constant pressure, we have-
$dQ = n{C_p}\vartriangle T$

This is path independent, hence it is a state function.

Heat at constant volume-

For heat at constant volume is equal to change in internal energy from the first law of thermodynamics. So, it is also a state function.
Therefore, among the following, only work-done in an isothermal process is not a state function.

Hence, the correct option is B.

Note: Whenever such types of questions appear, first understand what is a state function and then study each of the given processes to know whether these are path dependent or not. As mentioned in the solution, only work-done in an isothermal process is path dependent, hence it is not a state function.