Thermodynamics (from ancient Greek thermos 'warm' and dynamics 'power') also known as thermodynamics is a branch of classical physics. It is the doctrine of energy, its forms and their ability to do work.
The basis of thermodynamics is four main propositions. The thermodynamics brings quantities such as energy, heat, work, pressure and volume together. It allows us to find what changes are possible in a system and gives us information on the necessary steps on pressure temperature and other conditions. It gives no indication as to how fast the process happens or what happens at the microscopic level.
The foundations of thermodynamics were developed from the study of volume, pressure and temperature conditions in steam engines.The thermodynamics is also of great importance for the understanding and planning of processes in chemical plants, heat engines, as well as in heating and air conditioning.
Meaning of Termodynamic Equilibrium
In thermodynamics, a thermodynamic system is inside thermodynamic when it is in thermal equilibrium, mechanical equilibrium ,chemical etc. The thermodynamic is determined by values of different quantity such as pressure, temperature, etc. Specially thermodynamic equilibrium is a characterized by the minimum of thermodynamic potential, as Helmholtz free energy, ie Systems at constant temperature and the volume:
A = U - TS.
Or as Gibbs free energy, i.e. Systems at constant pressure and the temperature:
G = H - TS.
Thermodynamics deals with equilibrium states. The word implies a state of balance. In an state there are no unbalanced potentials (or driving) in the system. A system in equilibrium will undergoes no changes when it is isolated from its surroundings.
The concept of thermal can be understood in two different contexts.
Firstly, as a condition of a single thermodynamic system: It is in thermal equilibrium if it can be described by a few macroscopic quantities and if there sizes do not change over time. A bottle of soft drink in the refrigerator is in thermal because their condition is by weight, temperature, pressure, and alcohol is uniquely determined and (often) remains constant over time. A liter of boiling spaghetti water is not in thermal equilibrium, because necessary for the description of its turbulent flow motion gives us a lot of information about its state.
Second, as a relationship between multiple systems: Two bodies in thermal contact with each other, are each in thermal equilibrium if and only if they have the same temperatures.