Macroscopic and Microscopic Approach to Study Thermodynamics

Table of Contents

What are different approaches to study thermodynamics?

We can understand thermodynamics from two viewpoints (or approaches). One is microscopic and another is macroscopic.

Let us discuss each of them in detail. However, in Mechanical Engineering we only consider macroscopic approach.

Macroscopic (or Classical) view

In macroscopic approach we fix our attention to certain quantity of matter without considering the activities (or events) happening at molecular level.

In this approach we determine the properties (e.g. Pressure, Volume, Temperature) which get affected by the systems interaction with the surrounding.

There are some macroscopic properties which can be sensed by the human and some cannot.

Even the macroscopic properties which cannot be sensed by human can be related to the properties which can be sensed by the humans.

These relations can be established either by experiments or by theory at some macroscopic level.

Microscopic (or Statistical) view

In microscopic view we try to determine behavior of a system by the events happening at molecular level.

We can easily find that macroscopic behavior is always related to microscopic behavior because a matter is always comprised of molecules.

One can see that macroscopic behavior is an average of microscopic behavior of large number of molecules over a considerable period of time.

For example:

Pressure is a macroscopic property it can be sensed but it too has a microscopic explanation. Pressure can also be explained as the change of momentum due to molecular collision.

Difference in Macroscopic and Microscopic views of Thermodynamics

Table given below will help in understanding the differences in a better way.

Sr. No.	Macroscopic Approach	Microscopic approach
01	This approach is certain quantity of matter without the events happening at molecular level	Events happening at molecular level is taken into account
02	Macroscopic approach deals with the properties which can be sensed by humans. Or which can be obtained from mathematical relations.	A statistical approach is required for microscopic approach since number of molecules is very large
03	It is an averaged value of the activities happening at molecular level	These are real values and hence difficult to measure
04	In order to describe a system from macroscopic we need very less number of properties like pressure, volume, temperature etc.	In order to describe a system from microscopic approach we need a very large number of variables.