Question

Which of the following is not a state variable?
A. Pressure
B. Heat
C. Volume
D. Temperature

Answer 1

A state variable is a quantity that can be determined by the system's state at any given time. It is known as a variable that is only affected by the initial and final states, regardless of the middle state.

Complete answer:
By comparing state functions to path functions, state functions are defined. A state function is a property whose value is independent of the direction taken to achieve the function or value. In other words, if it's not a path function, it's most likely a state function.

Option A: Pressure depends upon the final and initial value. It is independent of the path. Hence, it is a state variable. Therefore, the option is incorrect.

Option B: Heat is transferred energy.We can't compare the initial and final value of heat, instead it is dependent on the path. Hence, this is not a state variable. Therefore, this option is correct.

Option C: Volume is a state function since it is determined only by the final and original values, not by the direction taken to arrive at those values. Any example that demonstrates this assertion is: Consider a balloon that has been inflated to a certain volume. It will achieve the same volume if inflated in several steps or in a single stage. As a consequence, since volume is independent of the object's direction or history, it is a state function. Therefore, the option is incorrect.

Option D: Temperature is a state function since it is one of the variables that is used to describe an object's state. Temperature is often affected by the final and original values, not the direction taken to arrive at those values. Therefore, the option is incorrect.

Hence, the correct answer is option B.

Note: In thermodynamics, state functions are often encountered; many of the equations used in thermodynamics are state functions. Furthermore, state functions are essential in thermodynamics since they simplify calculations and allow for the computation of data that would otherwise have to be collected by experiments.