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Principle of Chemical Process II ( 2nd law of thermodynamic and Enthropy) | Mr Abd Hamid's Profile

Week 11 to Week 13 (Second law of thermodynamics and entropy change)

Not all processes that obey the first law may occur spontaneously because the first law of thermodynamics only takes into consideration the conservation of the quantity of energy in the universe. However, in reality, the actual process only occurs in the direction of degradation of the quality of energy. Energy of higher quality is associated to higher temperature and lower entropy. Hence, at the end of the process, the quality of energy decreases, and the entropy of the universe increases.

Besides, the calculations of the thermal efficiency of heat engine and coefficient of performance (COP) of refrigeration cycle are also introduced. These are followed by the Carnot heat engine thermal efficiency and Carnot COP; these ideal devices are not existent but could be models for engineers to design the instruments with better performances. Moreover, with this in mind, maximum value of thermal efficiency or COP is no longer 100% but that of Carnot thermal efficiency or COP.

For any actual process, the entropy generation is always greater than zero; only for reversible processes, it is zero. If it is found to be less than zero, then the process is impossible.