Chapter 15 - Chapter 15 - Spontaneity, Entropy, and Free...

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Chapter 15 - Spontaneity, Entropy, and Free Energy 1 Spontaneous Processes 2 The Isothermal Expansion and Compression of an Ideal Gas 3 The Definition of Entropy 4 Entropy and Physical Changes 5 Entropy and the Second Law of Thermodynamics 6 The Effect of Temperature on Spontaneity 7 Free Energy 8 Entropy Changes in Chemical Reactions 9 Free Energy and Chemical Reactions 10 The Dependence of Free Energy on Pressure 11 Free Energy and Equilibrium 12 Free Energy and Work (skip) 13 Reversible and Irreversible Processes: A Summary (skip) 14 Adiabatic Processes (skip)
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Kinetics vs Thermo Thermodynamics predicts direction and “driving force”. Kinetics predicts speed (rate). Spontaneous Processes Occur on some timescale (maybe slowly) without outside intervention (examples: a battery will discharge, a hot cup of coffee will cool to ambient temperature). All spontaneous processes proceed toward “states” (macrostates) with the greatest number of accessible microstates.
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Microstates and Macrostates: An available microstate describes a specific detailed microscopic configuration (molecular rotations, translations, vibrations, electronic configuration) that a system can visit in the course of its fluctuations. A macrostate describes macroscopic properties such as temperature and pressure. For a gas at constant T: the number of available microstates increases with volume. For gas, liquid or solid, the number of available microstates increases with T (the number of available vibrational microstates, electronic microstates, etc. increases with T). When you heat anything, you increase the number of available microstates. When a liquid vaporizes, the number of available microstates increases. When a liquid freezes, the number of available microstates decreases.
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probable not probable This is not a spontaneous process. The reverse process (going from right to left) is spontaneous. a) A gas will spontaneously expand to fill the available space. b) There is a ‘driving’ force that causes a gas to spontaneously expand to fill a vacuum. c) The entropy of the universe increases with a gas expands to fill a vacuum. a=b=c What is a spontaneous process?
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probable not probable There are more available microstates on the right hand side than on the left hand side. If a system gains degrees of freedom (more constituents, more room to move, more available quantum states, more available rotational, vibrational, translational or electronic states), then it gains entropy. A spontaneous process increases entropy (but you must consider both the system and the surroundings) Why is this not a spontaneous process?
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The probability of occurrence of a particular arrangement (state) depends on the number of ways ( microstates ) in which that arrangement can be achieved. All microstates are equally probable. The probability of finding both molecules on the left side is ¼
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Chapter 15 - Chapter 15 - Spontaneity, Entropy, and Free...

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