CHEM 1120 Edition 1nd Lecture 28 Outline of Last Lecture I Spontaneity and Reversibility a Irreversible process II Entropy and the 2nd Law of Thermodynamics III Molecular Interpretations of entropy Outline of Current Lecture I Defining Entropy a Entropy as energy dispersal b Molecular Motion II Chemical Reactions and S Current Lecture I Defining Entropy a Positional Entropy where molecules are placed in space b Gas will spontaneously expand into a vacuum c 1 2 n gives probability all molecules are in one flask d Entropy as energy dispersal i Energy will try to disperse over a larger number of particles and energy levels ii 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 Motion i Translation molecule moves through space ii Rotation molecule spins around its center of gravity iii Vibration molecule changes it shape by bond stretching or bending iv Energy level spacing small to large translation rotation vibration electronic f The entropy S of a system is related to the number W of possible distributions of energy microstates among the energy levels of its molecules i 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 II g How does energy dispersal account for an increase in entropy with higher temperatures Higher temp more energy larger W greater S i Larger volume more closely spaced energy levels larger W greater S h Liquid molecules can translate rotate and vibrate molecules of a solid can only vibrate i Melting adds translational and rotational energies larger W larger S i Generally when a solid is dissolved in a solvent entropy increases i Less information is known Chemical Reactions and S a E cannot be measured but S can be measured b 3rd law of thermodynamics the entropy of a perfect crystal at 0 K is equal to 0
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