ABSTRACT
In thermodynamics, the specific region of interest is always denoted as the system. Everything else is referred to as the surroundings. Energy, such as heat and/or matter, may transfer between the system and surroundings. The thermodynamic state of a system is specified by a set of variables. For example, the change in the internal energy of a system can be expressed in terms of volume and entropy changes. In classical thermodynamics the system of interest is macroscopic and composed of a huge number of atoms. Temperature, T, is defined for the entire system based on its average kinetic energy. Entropy is a thermodynamic state function first introduced by Rudolph Clausius in the mid-1800s based on the working of heat engines. In order to understand entropy, the chapter considers the reversible isothermal expansion of a gas from some initial volume to some final volume.
