chapter 17 notes

chapter 17 notes - Chapter 17 Thermodynamics: Spontaneity,...

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©2010 Donald L. Siegel, All Rights Reserved Chapter 17 Chapter 17 Thermodynamics: Spontaneity, Entropy, and Free Energy
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©2010 Donald L. Siegel, All Rights Reserved Recap of Thermodynamics Recap of Thermodynamics (so far) (so far) W First Law Conservation of Energy – energy can neither be created nor destroyed “You can’t win” W What it says. Whether a reaction is endo- or exothermic W What it doesn’t say Whether a reaction will occur by itself
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©2010 Donald L. Siegel, All Rights Reserved Spontaneous Processes Spontaneous Processes W A process that occurs by itself is called spontaneous Object rolling down hill Gas escaping through a pinhole in a balloon W That something is spontaneous only says that something will happen, not how fast H 2 and O 2 in a container will from water, but without a spark to start it, it will take centuries for any water to form. W Non-spontaneous processes can occur, but not without help
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©2010 Donald L. Siegel, All Rights Reserved Spontaneity and Spontaneity and Exothermicity Exothermicity W Most, but not all, exothermic reactions are spontaneous Burning wood is spontaneous and exothermic Freezing water at room temperature is not spontaneous, but exothermic W Many endothermic processes are not spontaneous Converting water into H 2 and O 2 endothermic, not spontaneous Dissolving ammonium salts, spontaneous & endothermic
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©2010 Donald L. Siegel, All Rights Reserved How do we measure How do we measure spontaneity? spontaneity? W Order vs. chaos Entropy Measures randomness Number of arrangements Number of arrangements
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©2010 Donald L. Siegel, All Rights Reserved Example Example
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©2010 Donald L. Siegel, All Rights Reserved Entropy in action Entropy in action Consider 2 gases, each at 1 atm Open the stopcock separating them, and they mix Δ H = 0, Δ E = 0, so why do they mix? Increased disorder
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©2010 Donald L. Siegel, All Rights Reserved Entropy and the Second Law Entropy and the Second Law W In any spontaneous process, the entropy of the universe increases. W “You can’t break even” W Δ S univ = Δ S sys + Δ S surr System and surroundings are defined they way we did last semester in chapter 6 Now we have a numerical way to determine if a process is spontaneous
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©2010 Donald L. Siegel, All Rights Reserved
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This note was uploaded on 11/09/2011 for the course CHEM 162 taught by Professor Siegal during the Spring '08 term at Rutgers.

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chapter 17 notes - Chapter 17 Thermodynamics: Spontaneity,...

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