# What is the difference between classical thermodynamics and statistical mechanics? [duplicate]

What is the difference between classical thermodynamics and statistical mechanics?

To me, they are greatly different but are different approaches for explaining same thing. But I do prefer Statistical mechanics. The former deals in a macroscopic sense while the later investigates in a microscopic approach. It is evident in the definition of Second law given by them.

So, are there differences between the two? If so,what are they?

## marked as duplicate by ACuriousMind♦, Danu, JamalS, John Rennie, Kyle KanosJan 4 '15 at 17:18

• – glS Jan 4 '15 at 11:42

Statistical mechanics is more fundamental than thermodynamics: you can obtain classical thermodynamical results using statistical mechanics but not the reverse. Thus, they are not alternative explanations of the same phenomenon, but rather one is included in the other. Thus, even if we keep using the macroscopic results, we now understand that the macroscopic limit it is just a special limit case of a microscopic theory.

The name of these two subjects actually uncovers the difference. The classical mechanics doesn't involve microscopic concepts as temperature, heat capacity, entropy, etc. These terms are defined as a projection of statistical behaviour of the studied systems. The classical thermodynamics is more about measurements :-) and definitions.For instance, the statistical mechanics permits very accurate calculation of heat capacities (Cp and Cv) of simple molecules. In the case of classical thermodynamics, this is not possible ...