Thermodynamics - Introduction

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. 

Credit: http://fisitech.wordpress.com/content/thermodynamics/

Courtesy: W. R. Salzman (http://www.chem.arizona.edu) and http://thinkquest.org