Branch of physics and chemistry related to the study of thermal behavior of the body, the study of energy and its transformations (in particular the internal energy). 

Thermo. Thermodynamics studies the transformations of the systems (sets of body separated by a physical boundary or not) open or closed (depending on whether or not exchange matter with the outside) insulated or not (depending on whether or not exchange energy with the outside world) represented by state variables (intensive or extensive). 

The basic theoretical concepts of thermodynamics are the heat, the thermodynamic temperature, internal energy, the enthalpy, the entropy, reversibility. 

The experimental quantities are the heat capacity, pressure, volume, ... 

The principal laws of thermodynamics is the first principle, the second principle (V. Carnot and Clausius), (the third law of thermodynamics V. Nernst). 

The thermodynamic study of the body includes the design and validation of models of the thermal behavior of bodies, the equations of state, derived from experimental values. In practice, the equilibrium predicted by thermodynamics can be thwarted by the influence of time (to obtain the thermodynamic equilibrium might sometimes require a long time) and are governed by kinetics (cf. Arrhenius). In chemistry, equilibrium thermodynamics is the law of mass action (Guldberg V.).