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Lecture33_Notes_S

# Lecture33_Notes_S - Week 12 Lecture 33 Introduction Monday...

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Introduction Content Notes Suggested reading: SMITH, J.M. VAN NESS, H.C. and ABBOTT, M.M., Introduction to Chemical Engineering Thermodynamics , 7 th edition, McGraw-Hill Chapter 5 – pp. 159-170; 173-180 Why do we need the 2 nd Law of Thermodynamics? The First Law of Thermodynamics indicates that energy is conserved in a system (or in a process). We can however imagine processes which conserve energy but which never occur in nature. For example, if we put a cup of coffee into contact with a cold air, we observe that the hot object (the coffee) cools down and the cold object (the air) heats up until equilibrium is reached. The transfer of heat goes from the hot object to the cold object. t = 0 t = t equilibrium Based on the First Law, we can imagine a system in which the heat is instead transferred from the cold object to the hot object, and such a system does not violate the first law of thermodynamics. The cold object gets colder and the hot object gets hotter, but energy is conserved. Obviously we don't encounter such a system in nature. Some energy from the cold air will never be transferred back to the coffee to heat it up! t = 0 t = ? To explain this observation and other similar observations, the Second Law of Thermodynamics was proposed in various ways by Clasius, Kelvin, and Carnot.

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