Path Function and Point Function | Explained With Examples

By | February 19, 2018

For solving problems based on Thermodynamics, knowledge of path function and point function is necessary. Hence it is important to understand this concept properly.

Path function

A Path function is a function whose value depends on the path followed by a thermodynamic process, and not on the initial and final states of the system.
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 figure given above we can easily see that for the same initial and final state 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

Point function

A Point 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 change in temperature, change in pressure or change in temperature 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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