Thermodynamics: Definitions and the Zeroth Law

Introduction Thermodynamics is the science that has developed from the observations of the behavior of macroscopic systems. Keen observation and analysis of macroscopic systems led to some very general laws that form the basis of thermodynamics. It is worth mentioning that in most cases studies were made for some entirely different purpose but the analysis of the data from different experiments indicated some order and similarities that led to general laws of thermodynamics. For example, experiments carried out by Benjamin Thompson, (also called Count Rumford) on production of heat while boring holes in gunmetal for making cannons, for the first time clearly showed that heat is a form of energy that may be produced from work. Later, James P. Joule, British scientist, again through experiments established a relation between the mechanical work and the heat energy. The experiments of both Rumford and Joule contributed to the formulation of the first law of thermodynamics. In a similar way, French Engineer Nicolas Leonard Sadi Carnot, working for the improvement of the efficiency of steam engines, developed the well know Carnot cycle which laid the basis for the second law of thermodynamics. It may also be mentioned that the importance and physical significance of some of the common observations were realized much later, an example is the zeroth law of thermodynamics which was formulated much after the first three laws. The zeroth law, that defines the state of thermal equilibrium, was considered to be more fundamental than the already formulated three laws and was, therefore, assigned number zero in the hierarchy of thermodynamic laws. Like all other branches of science, thermodynamics also has its own terminology. Some of the terms frequently used in thermodynamics are defined here. System, Boundary and Surroundings Since it is not possible to observe whole of the universe at a time it is generally a part of the universe that is studied. The portion or part of the universe (which is under observation) enclosed by a boundary is called the system . The boundary of the system divides the universe into two parts, the system and the surroundings or the environment. In other words, system and surroundings make the universe.