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session_1_4 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY SPRING...

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1 M ASSACHUSETTS I NSTITUTE OF T ECHNOLOGY S PRING 2007 5.92 Energy Environment and Society (a Project Based First Year Subject supported by the d'Arbeloff Program) --------------------------------------------------------------------------------------- Session 1.4 . Energy Basics (continued) 1. Discussion of team projects and project selections 2. Summary of thermodynamics concepts and applications Readings and Assignments D. Goodstein, " Out of Gas " (Norton, 2004): Chapter 2, "Energy Myths and a Brief History of Energy", pp. 41 – 56 Practice Problems on First and Second Laws of Thermodynamics (due Feb. 21) Supplementary recommended text (on library reserve) J.B. Fenn, "Engines, Energy, and Entropy" (W.H. Freeman and Co., 1982) -------------------------------------------------------------------------------------------------------------------- Thermodynamics is about the flow of energy Thermodynamics was first developed to explain how much heat could be used to do work … eventually we learned that these laws apply to every material and energy transformation everywhere in the universe! Describes macroscopic properties of equilibrium systems (you don't need to know anything about atoms and molecules – but it helps!) Entirely Empirical (cannot be proven logically, but can be derived using statistical mechanics) Built on Four Laws and “simple” mathematics (but we will not assume you have had 18.02!) 0 th Law Defines Temperature (T) "The common sense Law" 1 st Law Defines Energy (U), Heat (q), Work (w) "You can break even, but you can't win" 2 nd Law Defines Entropy (S) "You have to go to 0 K to break even" "Everything wants to be as imperfect as possible" 3 rd Law Gives Numerical Value to Entropy "You can’t get to 0 K" (so you can never break even) These laws are UNIVERSALLY VALID , they cannot be circumvented .
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" From BTU's and calories Producing foot-pounds, ergs, and joules Heat Engines must, to serve our needs Obey inexorable rules." -- J.B. Fenn, "Engines, Energy, and Entropy" Definitions : System : The part of the Universe that we are interested in ( e v e r y t h i n g i n s i de the boundary) Surroundings : The rest of the Universe (everything else outside the boundary) Boundary : The surface dividing the System from the Surroundings BOUNDARY SYSTEM SURROUNDINGS 2
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In order to describe a system we have to specify a small number of macroscopic properties ("state variables"), such as Pressure p Energy U (or E) Volume V Enthalpy H Temperature T Entropy S Temperature is defined by the Zeroth Law of Thermodynamics: Thermal Equilibrium (when heat stops flowing) B B A B A 3 A When a hot object is placed in thermal contact with a cold object, heat flows from the warmer to the cooler object. This continues until they are in thermal equilibrium (no more heat flow). We say, at this point, that both bodies have the same “temperature”. This intuitively straightforward idea is formalized in the 0 th Law of thermodynamics and is made practical through the development of thermometers and temperature scales.
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This note was uploaded on 11/28/2011 for the course CHEM 5.74 taught by Professor Robertfield during the Spring '04 term at MIT.

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session_1_4 - MASSACHUSETTS INSTITUTE OF TECHNOLOGY SPRING...

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