Chapter 3 - Entropy: the second and third laws of thermodynamics

Abstract

First, we present examples for spontaneous changes, the difference between thermodynamic and kinetic stabilities, and a definition of entropy. Then, we examine the link between spontaneity and thermodynamic parameters. The principle of Clausius suggests that temperature has a role in the thermodynamics criterion of spontaneity. The study of Carnot's cycle helps to define efficiency, Kelvin scale and introduces the entropy basic equation. Entropy basics such as entropy equation, entropy and spontaneity, and statement of the second law are discussed. Calculating the entropy change for a change of state at a constant temperature, a perfect gas changing volume at a constant temperature, a substance being heated or cooled over a temperature range, an ideal gas undergoing an adiabatic change, and entropy change for a chemical reaction are presented and discussed. Furthermore, we exposed the relationship between entropy and probability, and develop an understanding of the third law of thermodynamics, absolute entropy equation, and entropy of mixing. This part concludes with an elaborate discussion on the relationships between entropy and other variables such as internal energy, enthalpy, temperature, pressure, and volume.