Thermodynamics is a macroscopic
theory. It deals with the bulk properties of matter. It does not
concern itself with whether or not there are atoms or molecules. In fact,
thermodynamics does not care whether or not there are atoms and molecules. Thermodynamics is the study of the patterns of energy change.
Thermodynamics refers to energy, and "dynamics" means the patterns of
change. Specifically the study of thermodynamics deals mainly with (1)
energy conversion and (2) the stability of molecules and direction of change.
On the other hand, quantum mechanics is a microscopic
theory because it deals with the individual particles of matter.
Statistical
thermodynamics brings us full circle by providing a mechanism for calculating
the properties of bulk material (macroscopic samples) from the properties
of the atoms and molecules which comprise the material.
Courtesy: W. R. Salzman (http://www.chem.arizona.edu) and http://thinkquest.org