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# 10.3 - Entropy and the 2nd law

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• at last your presentation makes me understand the concept of entropy. thank you

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### 10.3 - Entropy and the 2nd law

1. 1. THIS MEANS THAT THINGS FALL. THEY FALL FROM HEIGHTS OF ENERGY AND STRUCTURED INFORMATION INTO MATTER IS ENERGY. MEANINGLESS, POWERLESS DISORDER. ENERGY IS INFORMATION. EVERYTHING IS INFORMATION. PHYSICS SAYS THAT THIS IS CALLED STRUCTURES... BUILDINGS, SOCIETIES, IDEOLOGIES... ENTROPY. WILL SEEK THEIR POINT OF LEAST ENERGY.Entropy (S) = a measure of randomness or disorder
2. 2. Entropy It’s just a measure of disorderPhysics classrooms are full of Entropy!
3. 3. Entropy and your bedroom Low Entropy High Entropy
4. 4. No matter what wesay or try, the entropyof the universe isincreasing!
5. 5. The molecules in the solid are in a much morerestricted or ordered state so they have lowentropy.
6. 6. Entropy increases when melting.Entropy decreases when freezing
7. 7. What happens to entropy when a machine does work? ΔS ↓ ΔS ↑
8. 8. Refrigerators Room ΔS ↑ ΔS ↓The heat pump in the fridge The entropy of thedoes work to reduce the room increases byentropy inside it. more.
9. 9. What happens to the temperature of theroom? The temperature of the room increases .
10. 10. Entropy Increases with...• Melting (fusion) Sliquid > Ssolid• Vaporization Sgas > Sliquid• Heating ST2 > ST1 if T2 > T1• Dissolving (usually) Ssolution > (Ssolvent + Ssolute)• Molecular complexity more bonds, more entropy• Atomic complexity more e-, protons, neutrons
11. 11. Entropy Curve Solid Liquid Gas S ← vaporizationEntropy ← fusion 0 0 Temperature (K)
12. 12. The Statistics of EntropyAnother way to think about entropy isthat being disordered is just morelikely. It’s just chance
13. 13. A box containing air molecules, divided in two compartmentswith a hole in the dividing wall. Since there are many moremolecules in the left compartment, there will also be manymore molecules crossing the divide from left to right.The second law of thermodynamics states that in an isolated systemthe entropy will increase.In the statistical definition of entropy according to Boltzmann, thismeans that the system will evolve to its most probable state.
14. 14. Entropy, Marble Example• Suppose you have a bag with 50 red marbles and 50 green marbles• You draw a marble, record its color, return it to the bag, and draw another• Continue until four marbles have been drawn• What are the possible results and what are their probabilities?
15. 15. Entropy, Marble Example,Results • The most ordered are the least likely • The most disorder is the most likely
16. 16. Entropy & TimeBecause systems move from order todisorder, time has a direction.
17. 17. Which came first?
18. 18. Entropy and Life Life is an entropy reducerDoes this break the second law of thermodynamics?