110121 - 2nd Law of TD Entropy(Chapter 4 p 81-86...

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1 CHM3400 - Lecture 7 Jan 21 2 nd Law of TD: Entropy (Chapter 4 p. 81-86) • Spontaneous processes (examples) • Entropy (= disorder) (probability, heat flow) • 2 nd Law of Thermodynamics

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2 Examples Example 1 : bouncing ball Kinetic energy of a bouncing ball is converted into thermal energy of the floor. http://www.chem.uci.edu/undergrad/applets/bounce/bounce.htm Thermal energy of the floor is converted into kinetic energy of the ball. Neither of these processes violates the 1 st Law of TD, but only one is observed .
3 Example 2 : heat exchange Again, while both of these processes are possible accoring to the 1 st Law of TD, only one is actually observed. When you bring two pieces of metal (of different temperatures) in thermal contact, which way will the heat flow? T = 1000 K T = 300 K q (heat) ? Examples

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4 Example 3 : gas expansion V 2 Let gas expand from initial volume V 1 into volume V 2 ; Note (V 1 +V 2 )/V 1 = 2xV 1 . Gas will expand to occupy both V 1 and V 2 . Is it possible that we observe the reverse process spontaneously? It’s a matter of statistics : If we had one particle, what are the odds of finding it in V 1 ? ½ Probability If we had two particles, what are the odds of finding both in V 1 ? ½ x ½ = ¼
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110121 - 2nd Law of TD Entropy(Chapter 4 p 81-86...

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