The Second and Third Laws

Abstract

The second law of thermodynamics and the introduction of a state function named entropy are the main themes. A tiny bit of relevant history is told, including the accomplishments of the fantastic Sadi Carnot (Carnot cycle) and the monumental scientists Rudolf Clausius and William Thomson (Lord Kelvin). Together with the first law, the second law makes possible the establishment of a criterion for the spontaneity of processes. This formulation is beautifully general, and it is based on the Clausius inequality principle which states that a process which shows a positive entropy production (i.e. the sum of the entropy changes of a given system and its surroundings) is spontaneous. The third law of thermodynamics, also referred to as the Nernst heat theorem, gives entropy an absolute scale..