Laws Of Thermodynamics

Zeroth Law:
This law recognizes that if two systems are in thermal equilibrium with a third, they are also in thermal equilibrium with each other, thus supporting the notions of temperature and heat.

First Law:
This law distinguishes between two kinds of physical process, namely energy transfer as work, and energy transfer as heat. It tells how this shows the existence of a mathematical quantity called the internal energy of a system. The internal energy obeys the principle of conservation of energy but work and heat are not defined as separately conserved quantities. Equivalently, the first law of thermodynamics states that perpetual motion machines of the first kind are impossible.

Second Law:
This law distinguishes between reversible and irreversible physical processes. It tells how this shows the existence of a mathematical quantity called the entropy of a system, and thus it expresses the irreversibility of actual physical processes by the statement that the entropy of an isolated macroscopic system never decreases. Equivalently, perpetual motion machines of the second kind are impossible.

Third Law:
This law concerns the entropy of a perfect crystal at absolute zero temperature, and implies that it is impossible to cool a system to exactly absolute zero, or, equivalently, that perpetual motion machines of the third kind are impossible.

History:
In about 1797, Count Rumford (born Benjamin Thompson) showed that mechanical action can generate indefinitely large amounts of heat, so challenging the caloric theory. The historically first established thermodynamic principle which eventually became the second law of thermodynamics was formulated by Sadi Carnot during 1824. By 1860, as formalized in the works of those such as Rudolf Clausius and William Thomson, two established principles of thermodynamics had evolved, the first principle and the second principle, later restated as thermodynamic laws. By 1873, for example, thermodynamicist Josiah Willard Gibbs, in his memoir Graphical Methods in the Thermodynamics of Fluids, clearly stated the first two absolute laws of thermodynamics. Some textbooks throughout the 20th century have numbered the laws differently. In some fields removed from chemistry, the second law was considered to deal with the efficiency of heat engines only, whereas what was called the third law dealt with entropy increases. Directly defining zero points for entropy calculations was not considered to be a law. Gradually, this separation was combined into the second law and the modern third law was widely adopted.