What is the difference between classical thermodynamics and statistical thermodynamics?

Classical thermodynamics was developed before atoms were fully understood.

There are two approaches to study behaviour of matter:

1. The macroscopic approach [classical thermodynamics]

2. The microscopic approach [statistical thermodynamics]

In macroscopic approach a certain quantity of matter is chosen from study and not much attention is given to what is happening at molecular levels.

Whereas, in the microscopic approach detailed are taken into account at molecular level such as position, velocity, energy of each molecule and the behaviour of whole is given from summing up behaviour of each molecule.

The macroscopic approach is only concerned with effects of actions of many molecules and these effects can be perceived by humans senses.

All the results of the classical or macroscopic thermodynamics can be derived from microscopic or statistical study of matter.