F09_230_L10pre - CHEM 230 F09 Lecture 10 Chapter 7:...

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Unformatted text preview: CHEM 230 F09 Lecture 10 Chapter 7: Thermodynamics the Second and Third Laws Session ID: 230 Outline Entropy Thermochemical entropy = sharing of energy among microstates Defining microstate via quantized translational, rotational, and vibrational energy S = k B ln(#microstates) = k B lnW Effects of heat and volume Measuring Entropy S = q rev /T Constant Temperature phase change S = H/T volume change S = nRln(V 2 /V 1 ) pressure change: S = nRln(P 1 /P 2 ) Constant Volume S = nCln(T 2 /T 1 Outline Entropy Thermochemical entropy = sharing of energy among microstates Defining microstate via quantized translational, rotational, and vibrational energy S = k B ln(#microstates) = k B lnW Effects of heat and volume Measuring Entropy S = q rev /T Constant Temperature phase change S = H/T volume change S = nRln(V 2 /V 1 ) pressure change: S = nRln(P 1 /P 2 ) Constant Volume S = nCln(T 2 /T 1 ) Spontaneous Change Has a tendency to occur without needing to be driven by an external influence. Happens fast of slow. Can require energy or give off energy. hot cold Entropy = Disorder Entropy = measurement of probability Entropy of isolated system increases in spontaneous change (~2nd Law) High entropy High disorder High probability Low entropy High order Low probability Natural progression Thermodynamic Entropy = Sharing Entropy is a measure of the degree of spreading and sharing of thermal energy within a system This spreading and sharing can be spreading of the thermal energy into a larger volume or its sharing amongst previously inaccessible microstates of the system. Microstates: Molecular Motion Translational: molecules moving Rotational Vibrational z -axis x-axis y-axis z -axis H O H x-axis y-axis H O H H O H H O H H O H H O H H O H stretching change in bond angle Concept Question Which modes of molecular motion are prevalent in crystalline solids ? Choose all that apply....
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F09_230_L10pre - CHEM 230 F09 Lecture 10 Chapter 7:...

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