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Differentiate between macroscopic and microscopic approaches. Which approach is used in the study of engineering thermodynamics.Or Explain the macroscopic and microscopic point of view.

Answer»

Thermodynamic studies are undertaken by the following two different approaches.  Macroscopic approach–(Macro mean big or total)

 Microscopic approach–(Micro means small)

 The state or condition of the system can be completely described by measured values of pressure, temperature and volume which are called macroscopic or time–averaged variables. In the classical

thermodynamics, macroscopic approach is followed. The results obtained are of sufficient accuracy and validity. Statistical thermodynamics adopts microscopic approach. It is based on kinetic theory. The matter consists of a large number of molecules, which move, randomly in chaotic fashion. At a particular moment, each molecule has a definite position, velocity and energy. The characteristics change very frequently due to collision between molecules. The overall behaviour of the matter is predicted by statistically averaging the behaviour of individual molecules. 

Microscopic view helps to gain deeper understanding of the laws of thermodynamics. However, it is rather complex, cumbersome and time consuming. Engineering thermodynamic analysis is macroscopic and most of the analysis is made by it. 

These approaches are discussed (in a comparative way) below:

Macroscopic approachMicroscopic approach
1. In this approach a certain quantity of matter is considered without taking into account the events occurring at molecular level. In other words this approach to thermodynamics is concerned with gross or overall behaviour. This is known as classical thermodynamics.
2.The analysis of macroscopic system requires simple mathematical formulae.
3.The values of the properties of the system are their average values. For example, consider a sample of a gas in a closed container. The pressure of the gas is the average value of the pressure exerted by millions of individual molecules. Similarly the temperature of this gas is the average value of transnational kinetic energies of millions of individual molecules. these properties like pressure and temperature can be measured very easily. The changes in properties can be felt by our senses.
4.In order to describe a system only a few properties are needed.		1. The approach considers that the system is made up of a very large number of discrete particles known as molecules. These molecules have different velocities and energies. The values of these energies are constantly changing with time. This approach to thermodynamics, which is concerned directly with the structure of the matter, is known as statistical thermodynamics.
 2. The behaviour of the system is found by using statistical methods, as the number of molecules is very large. so advanced statistical and mathematical methods are needed to explain the changes in the system.
3. The properties like velocity, momentum, impulse, kinetic energy, and instruments cannot easily measure force of impact etc. that describe the molecule. Our senses cannot feel them.
  4. Large numbers of variables are needed to describe a system. So the approach is complicated.


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