Thermodynamics is the study of energy exchange relationships involving heat and mechanical work. Broken down into its constituent fractions, the term thermodynamics means heat motion. It is the branch of physics dealing with the reversible conversion of heat energy into other forms, particularly mechanical energy. In order to discuss the behavior of heat energy in physical systems, the distinction between heat and temperature must be made.

Heat and temperature are fundamentally different quantities. The concept of heat can be understood on the basis of microscopic mechanical energy. Heat is the kinetic energy (energy of movement) and potential energy (energy in an inactive form) of the individual molecules of a material. More exactly, heat is the sum of all of the kinetic and potential energies of the particles in a quantity of matter. Temperature, then, is a measure of the average kinetic energy of the...