CH8Notes - Chapter Eight Thermodynamics: The Second and...

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Chapter Eight Thermodynamics: The Second and Third Laws CHEM 1211K Fall 2010 1
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Objectives Develop an understanding of spontaneity and entropy. Entropy changes accompanying changes in physical state Develop a molecular interpretation of entropy Examine the equivalence of statistical and thermodynamic entropy Understand how entropy of a system and entropy of surroundings is related. Be able to work with Gibbs free energy and relate it to spontaneity Understand the effect of temperature on Gibbs free energy Explore the relationship between Gibbs free energy and equilibrium 2
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Key Ideas The direction of natural change corresponds to the increasing disorder of energy and matter. Disorder is measured by the thermodynamic quantity called entropy. A related quantity—Gibbs free energy— provides a link between thermodynamics and the description of chemical equilibrium 3
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Why is it important? The second law of thermodynamics is the key to understanding why on chemical reaction has a natural tendency to occur by another one does not. The third law of thermodynamics is the basis of the numerical values of entropy and Gibbs free energy. The second and third laws jointly provide a way to predict the effects of changes in temperature and pressure on physical and chemical processes. 4
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Spontaneous Change (8.1) A spontaneous change is one that has a tendency to occur without needing to be driven by an external influence. 5 Figure 8.1 http://tinyurl.com/3y7optb http://tinyurl.com/36xqclx http://tinyurl.com/3ycnu2t
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Section summary: A process is spontaneous if it has a tendency to occur without being driven by an external influence. Spontaneous changes need not be fast. 6 Spontaneous Change (8.1)
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Entropy and Disorder (8.2) Energy and matter tend to disperse in a disorderly fashion. Cooling of a hot block of metal Expansion of a gas 7
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Entropy , S, is a measure of disorder. The entropy of an isolated system increases in the course of any spontaneous change. Entropy is a state function. 8 Entropy and Disorder (8.2)
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The second law of thermodynamics states that the natural progression of a system and its surroundings (which together make up the universe ) is: 9 Entropy and Disorder (8.2)
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At constant temperature: 10 Entropy and Disorder (8.2) S = q rev T
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Section summary: Entropy is a measure of disorder. According to the second law of thermodynamics, the entropy of an isolated system increases in any spontaneous process. Entropy is a state function. 11 Entropy and Disorder (8.2)
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We can use to derive an equation to calculate the entropy change when a system is heated . 12
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This note was uploaded on 01/16/2012 for the course CHEM 1211 taught by Professor Ford during the Fall '09 term at Georgia Institute of Technology.

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CH8Notes - Chapter Eight Thermodynamics: The Second and...

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