Path Function & Point Function | Explained With Examples

By | February 19, 2018

Table of Contents

Path function

A Path function is a function whose value depends on the path followed by the thermodynamic process irrespective of the initial and final states of the process.
An example of path function is work done in a thermodynamic process.
Work done in a thermodynamic process is dependent on the path followed by the process.
A path function is an inexact or imperfect differential.
 
diagram to illustrate path function and point function
In the P-V diagram given above we can easily see that for the same initial and final states of the system, work done in all the three process is different.
For process A work done is b2A1a
For process B work done is b2B1a
For process C work done is b2C1a
Another example of path function is heat.

Point function

A Point function (or state function) is a function whose value depends on the final and initial states of the thermodynamic process, irrespective of the path followed by the process.
Example of point functions are temperature, pressure and entropy etc.
A point function is a property of the system or we can say all the properties of the system are point functions.
Point functions are exact or perfect differential.
Note: Since a point function is only dependent on the initial or final state of the system, hence in a cyclic process value of a thermodynamic function is zero, or change in thermodynamic property is zero.

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