CHEM 1120 1nd Edition Lecture 28Outline of Last Lecture I. Spontaneity and Reversibilitya. Irreversible processII. Entropy and the 2nd Law of ThermodynamicsIII. Molecular Interpretations of entropyOutline of Current Lecture I. Defining Entropya. Entropy as energy dispersalb. Molecular MotionII. Chemical Reactions and ΔSCurrent LectureI. Defining Entropya. “Positional” Entropy-where molecules are placed in spaceb. Gas will spontaneously expand into a vacuumc. (1/2)^n gives probability all molecules are in one flaskd. Entropy as energy dispersali. Energy will try to disperse over a larger number of particles and energy levelsii. More probably that energy will disperse over many particles than to be concentrated in a few iii. Probability that heat will not disperse is nil e. Molecular Motioni. Translation: molecule moves through spaceii. Rotation” molecule spins around its center of gravityiii. Vibration: molecule changes it shape by bond stretching or bendingiv. Energy level spacing=small to large: translation < rotation < vibration < electronicf. The entropy, S, of a system is related to the number (W) of possible distributions of energy (microstates) among the energy levels of its moleculesi. S = k x ln(W)1. k = Boltzmann constant = 1.381 x 10^-23 J/K These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.g. How does energy dispersal account for an increase in entropy with higher temperatures? Higher temp more energy larger W greater Si. Larger volume more closely spaced energy levels larger W greater Sh. Liquid molecules can translate, rotate, and vibrate, molecules of a solid can only vibrate i. Melting adds translational and rotational energies larger W larger Si. Generally, when a solid is dissolved in a solvent entropy increasesi. Less information is known II. Chemical Reactions and ΔSa. E cannot be measured, but S can be measuredb. 3rd law of thermodynamics: the entropy of a perfect crystal at 0 K is equal to
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