Examples of path function - Thermodynamics

Q.  Which of the following is NOT a path function?
- Published on 20 Aug 15

a. Internal energy
b. Heat energy
c. Work energy
d. none of the above

ANSWER: Internal energy
In thermodynamics, energy can be in two forms, energy in transit and energy in storage. Energy in transit is a path function as the transfer of this energy through the boundaries of the system depends on the path which is followed by the system in the process. But energy in storage does not cross the boundaries of the system; hence it is a point function. Heat transfer as well as work transfer between the system and surrounding depends upon the path by which the process is occurred. Therefore heat energy and work energy are the path functions. Energy in storage is the internal energy. The change in internal energy (ΔE) remains constant, no matter which path is followed by a system to undergo a change of a certain state. Thus internal energy is a point function or state function.

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