Introduction

The four laws of thermodynamics and some of their implications have been discussed in the previous chapters. In this chapter we shall study the applications of the principles of thermodynamics to some problems of physics and engineering. Thermodynamics is frequently used for the analysis of chemical reactions. However, the sign convention used in chemistry for defining work and other thermodynamic functions is different than that used in physics, and, therefore, the application of thermodynamics to chemical reactions, also called thermochemistry, will be dealt separately to avoid any confusion.

Pedagogic development of thermodynamics suggested that it can be applied only to gases, liquids and to some extent to solids. However, thermodynamics has a very wide scope of applications and can be applied to any macroscopic system, irrespective of it being a solid, liquid, gas, radiations, magnetic, or electric system etc. The following examples are chosen to illustrate the methodology of applying thermodynamics to other systems.

The Blackbody Radiation

Blackbody radiation is an idealized concept of a bundle of radiations consisting of electromagnetic waves of all frequencies from zero to infinity with a well-defined strength of each frequency component at a given temperature. Such radiation is assumed to be emitted when a so-called blackbody is heated. A blackbody is a body that absorbs all electromagnetic radiations that fall on it and emits them all on heating. Many attempts, some highly technical and sophisticated have been made to build a blackbody, but a simple one can be made by taking a spherical hollow ball like body with a small hole, the interior of which is painted black. A conical projection opposite to the hole scatters the radiations entering the ball through the hole which are absorbed by the blackened walls. Thus essentially all radiations falling at the hole of the body are absorbed by the inside walls and none is able to come out through the opening making the ball a blackbody for incident radiations. If the ball is made of a material that may withstand high temperature, the interior of the ball (also called the cavity) will be filled with electromagnetic radiations characteristic of blackbody radiation at that temperature to which the body is heated.