Chapter+20 - Chapter 20 Thermodynamics: Entropy, Free...

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Click to edit Master subtitle style 6/6/11 Dr. Shamindri M. Arachchige arachsm@vt.edu Davidson 11 1 Office Hours: Location: Davidson 11 Monday 1:45-5:00 PM Wednesday 1:45-4:15 PM Other hours by appointment 11 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions
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6/6/11 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions Thermodynamics: Spontaneous Reactions: Nonspontaneous Reactions: If a reaction is spontaneous in one direction, it is not spontaneous in the reverse direction. Study of energy changes in a system (transformation of energy from one form to another). Reaction that proceeds without continued outside help. Once initiated, the reactions happens on its own. Reactions that require continued outside support. 22
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6/6/11 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions Examples: Spontaneous reactions may be fast: 2H 2 (g) + O 2 (g) 2H 2 O( g ) H = -483.6 kJ   Or, spontaneous reactions may be slow: 2Fe(s) + 3/2O 2 (g) + 3H 2 O( l ) 2Fe(OH) 3 (s) H = -780.6 kJ 33
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6/6/11 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions FACTORS AFFECTING SPONTANEITY 1. Enthalpy, H: H = – : Exothermic; heat is released by the system into the surroundings. Products have less energy than the reactants. Most exothermic reactions are spontaneous at room temperature: H = + : Endothermic; heat is absorbed by the system from the surroundings. Products have more energy than the reactants. Some endothermic reactions are also spontaneous 44
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6/6/11 55 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions 2. Entropy (S) : Entropy of substances: how disordered are the atoms, molecules, etc.: B e f o r e M i x i n g A f t e r M i x i n g G a s A G a s B
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6/6/11 66 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions s o l i d l i q u i d l i q u i d g a s s o l u t e s o l v e n t s o l u t i o n + M e l t i n g : S > S l i q u i d s o l i d V a p o r i z a t i o n : S > S v a p o r l i q u i d D i s s o l v i n g : S > ( S + S s o l n s o l v e n t s o l u t e )
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6/6/11 77 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions Temperature changes So increases as the temperature rises (more thermal disorder, more motion of particles).
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88 Chapter 20 Thermodynamics: Entropy, Free Energy, and the Direction of Chemical Reactions Example Problem : Do the following processes lead to an increase in entropy ( S = +) or to a decrease in entropy ( S = –)? a.
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This note was uploaded on 06/06/2011 for the course CHEM 1036 taught by Professor Amateis during the Spring '08 term at Virginia Tech.

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Chapter+20 - Chapter 20 Thermodynamics: Entropy, Free...

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