ABSTRACT
This chapter derives one of the most important equations in thermodynamics, the so called Clapeyron Equation, named after Paul Emile Clapeyron, one of the founders of thermodynamics. The Clapeyron equation is magical in its ability to explain a myriad of facts concerning phase equilibria. There are many demonstrations of the Clapeyron equation available. Some of them may appear much ’simpler’ than the one presented. But on closer examination, one would find that in such proofs some seemingly reasonable facts are assumed. As a first application of the Clapeyron equation, let consider the so called freezing curves. These are the coexistence curves for a solid-liquid coexistence. In a majority of cases, it requires heat to take the solid to a liquid. The chapter discusses a classic application of the Clausius-Clapeyron approximation to the phenomena of Dew and Frost. This is the phenomemon which manifests, for example, as beautiful water droplets condensing on various surfaces on a cold morning.
