Entropy and The Second Law of Thermodynamics

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Physics Fluid Mechanics and Thermal Physics

	The Second Law Revisited:
	For a given thermodynamic system, the number of available macro states is accessible. Among these macro states, it is assumed that all have equal probability of occurrence. Most of these macro states are disordered. All of the physical processes that take place in a system tend to cause the system and its surroundings to move towards more probable macro states and hence towards randomness. Thus, the entropy of the system increases. Hence, it can be concluded that the entropy of the universe increases in all real processes. This statement is equivalent to that of Kelvin-Planck and Clausius statements. A Statistical View of Entropy: In the statistical point of view a given macro state can have a number of microstates so that the entropy can be considered as the measure of microscopic disorder. And there is more number of disordered microstates than the ordered ones. For a given macro state, the entropy can be connected with the number of microstates as: where k_B is the Boltz-mann constant and W is the number of microstates available to the system for the existing macro state. Because of the statistical tendency of systems to proceed towards the states of greater probability and greater disorder, all natural processes are irreversible, and for them the entropy increases.