Lecture5 - Take Home Lessons Thermodynamics Simple Elegant...

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1 Chapter 20 Thermodynamics: Entropy, Free Energy and the Direction of Chemical Reactions “Take Home Lessons” Thermodynamics: Simple Elegant Relations that Teach Us the Directions of Reactions and Maximum Extractable Work Entropy makes the world go round Entropy is simply the number of different possible permutations/probability to have certain arrangement of atoms AND energy Entropy also referred to as disorder Entropy 0 (always increases iff change) Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions 20.1 The Second Law of Thermodynamics: Predicting Spontaneous Change energy/heat needed …. Probability of gaining net energy to drive reaction related to entropy (Second Law of Thermodynamics Δ S>0) 20.2 Calculating the Change in Entropy of a Reaction (Third Law of Thermodynamics S=0 at T=0 absolute determination of entropy) 20.3 Entropy, Free Energy, and Work 20.4 Free Energy, Equilibrium, and Reaction Direction { “Suggested” Problems: Chapter 20: 2, 5, 10, 12,16,18, 20, 22, 24, 26, 28, 31, 33, 37, 46, 56, 58, 62, 64, 65, 66, 68, 72, 78, 80, 83, 87, 96, 99,104,106,110 Be sure to be understand free energies and connection to entropy. Develop facility to use free energies, entropy, enthalpies to predict reaction direction from starting conditions and maximum work/energy that can extracted
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2 Limitations of the First Law of Thermodynamics Δ E = q + w E universe = E system + E surroundings Δ E system = - Δ E surroundings The total energy-mass of the universe is constant. Clearly the First Law does not tell us anything about the direction of change in the universe…. Really need to know what is the probability of gaining sufficient energy for a reaction AND probability of forming reactive complex…. .for whole system Δ E system + Δ E surroundings = 0 = Δ E universe Initially thought that all “spontaneous” reactions were exothermic or produce heat (viz formation of stronger bonds) e.g. combustion, explosions…Nature goes downhill
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This note was uploaded on 04/18/2011 for the course CHM 151 taught by Professor Dong during the Winter '08 term at University of Toronto.

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Lecture5 - Take Home Lessons Thermodynamics Simple Elegant...

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