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.
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.