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230_Sp10_L09_post-1

# 230_Sp10_L09_post-1 - CHEM 230 Sp10 Lecture 09 Chapter 7...

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CHEM 230 Sp10 Lecture 09 Chapter 7: Entropy 1) Statistics 2) Microstates 3) What changes entropy? Session ID: 230

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What is Entropy? 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.

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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
Energy Quantization Energy is quantized not continuous Example: energy levels of electrons vibrational rotational translational lots of lines

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Example: 3 particles in a system with a total energy of 3 Note: Distinguish between particles http://www.chem1.com/acad/webtext/thermeq/TE1.html#SEC3 Distribute molecules among energy levels
A microstate Imagine that you could take an instantaneous snapshot of the energy of all the individual molecules in a flask. Each molecule's energy is quantized on a particular energy level. Each accessible energy level (at T and V) could have zero, one, or many molecules "on it".

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