Introduction

Classical thermodynamics is a phenomenological description of nature. The mathematical relationships of thermodynamics are precise, but they do not tell us the molecular origin of the properties of matter. This chapter discusses a means of gaining a molecular interpretation of thermodynamic quantities. If you've spotted a trend we set from page one of this book, you will have guessed that mathematics will play an important role here. The required mathematical background certainly is greater than earlier on, but not substantially so. And, as before, all the main ideas can be expressed relatively well in figures or words. Though it is of course important to be able to use the mathematics, what is far more important is to have a good sense of what the mathematics says! Indeed, this is what distinguishes the physical biochemist from the mathematician. One should always bear in mind that although mathematics applies to everything, it is the physical biochemist who hires the mathematician, not the mathematician who hires the physical biochemist.

The need for a rethinking of the foundations of thermodynamics was first realized when the work of British chemist and physicist John Dalton (1766–1844) and Russian chemist Dmitri Ivanovich Mendele'ev (1834–1907) on the atomic theory of matter began to be widely accepted after the middle of the nineteenth century. Classical thermodynamics is built on the tacit assumption that many particles are present, and it deals with macroscopic properties of such collections of particles.