seclawthermo - Second law of thermodynamics heat engines...

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Second law of thermodynamics & heat engines Some processes one might imagine obey the first law of thermodynamics but still do not happen. For example, heat flows spontaneously from hot to cold but not from cold to hot even though this would conserve energy too. Other examples include ageing, dropping an egg, etc. . The second law of thermodynamics shows why some imaginable things do not happen even though they conserve energy. In short, the second law concerns ordered and disordered forms of energy. The mathematical statement of the second law comes in various forms. Sometimes it is stated in terms of entropy and other times in terms of heat engines. • ∆ S isolated > 0 (a statement of entropy non -conservation) It is impossible for a heat engine to have 100% efficiency. But what is entropy , S? The way this is defined in thermodynamics is very precise:
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S dQ/T , where T must be in Kelvin. rev Notice the integral assumes a reversible process. A
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