Macroscopic and Microscopic approaches - Thermodynamics:
Thermodynamic studies are undertaken by following two different approaches.
l. Macroscopic approach (Macro mean big)
2. Microscopic approach (Micro means small)
The state or condition of system can be described completely by measured values of pressure, temperature and volume that are called macroscopic or time averaged variables. In classical
thermodynamics, macroscopic approach is considered. The results obtained are of adequate accuracy and validity.
Statistical thermodynamics uses microscopic approach. It is based on the kinetic theory. The matter consists of large number of molecules that move randomly in chaotic fashion. At particular moment, each molecule has a specific position, velocity and energy. The characteristics change very frequently because of collision between molecules. The overall behavior of matter is predicted by statistically averaging the behavior of individual molecules.
Microscopic view helps to gain better understanding of the laws of thermodynamics. But, it is rather complex, cumbersome and time consuming. Engineering thermodynamic study is macroscopic and most of analysis is made by it.
These approaches are discussed below:
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Macroscopic approach
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Microscopic approach
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1. In this approach certain quantity of matter is considered without taking into account the events taking place at molecular level. Or we can say that this approach to thermodynamics is concerned with gross or overall behavior. This is called as classical thermodynamics.
2. The analysis of macroscopic system requires easy mathematical formulae.
3. The values of properties of system are their average values. For instance, consider a sample of gas in a closed container. The pressure of gas is the average value of pressure exerted by millions of individual molecules. Likewise the temperature of this gas is the average value of transnational kinetic energies of millions of individual molecules. These properties such as pressure and temperature can be measured easily. The changes in properties can be felt by us.
4. In order to describe system only a few properties are required.
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1. The approach considers that system is made up of a very large number of discrete particles called as molecules. These molecules are having different velocities and energies. The values of these energies are changing constantly with time. This approach to thermodynamics that is concerned directly with structure of matter is called as statistical thermodynamics.
2. The behavior of system is can be determined by using statistical methods, as number of molecules is very large. So superior statistical and mathematical methods are required to explain the changes in the system.
3. The properties such as velocity, impulse, kinetic energy, momentum, and instruments cannot be easily measure force of impact etc. which describe the molecule. We cannot feel them.
4. Large numbers of variables are required to describe a system. Thus the approach is complicated.
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