Microscopic models for thermodynamics

Abstract

The presentation of elementary thermodynamics for engineering students using microscopic models based on classical mechanics is discussed. It is argued that it is a first approximation to the microscopic structure of matter and a good application of the classical mechanics of particle systems. The model of classical particles is used to deduce the state equation of an ideal gas, understand the pressure and relate the absolute temperature with the mean kinetic energy per molecule. The theorems of work and mechanical energy are used to understand the thermodynamic concepts of internal energy, heat and work, and to reobtain the first principle of thermodynamics. The entropy is presented as a function proportional to the logarithm of the enormous number of possible microstates for a given macroscopic state. Starting from this definition and postulating the increasing of entropy when the system evolve towards equilibrium the usual presentation of the second principle is reobtained.