10.3 - entropy and the 2nd law
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MATTER IS ENERGY.
ENERGY IS INFORMATION.
EVERYTHING IS INFORMATION.
PHYSICS SAYS THAT
STRUCTURES...
BUILDINGS, SOCIETIES,
IDEOLOGIES... WILL SEEK
THEIR POINT OF LEAST
ENERGY.
THIS MEANS THAT
THINGS FALL.
THEY FALL FROM HEIGHTS
OF ENERGY AND
STRUCTURED INFORMATION
INTO MEANINGLESS,
POWERLESS DISORDER.
THIS IS CALLED
ENTROPY.
Entropy (S) = a measure of randomness or disorder
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Entropy
It’s just a measure of disorder
Physics classrooms are full of Entropy!
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Entropy and your bedroom
Low Entropy High Entropy
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No matter what we say or try, the entropy of the universe is increasing!
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The molecules in the solid are in a much more restricted or ordered state so they have low entropy.
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Entropy increases when melting.
Entropy decreases when freezing
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What happens to entropy when a machine does work?
ΔS ↓
ΔS ↑
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Refrigerators
Room
ΔS ↓
ΔS ↑
The heat pump in the fridge does work to reduce the entropy inside it.
The entropy of the room increases by more.
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What happens to the temperature of the room?
The temperature of the room increases .
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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
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Entropy Curve
Solid GasLiquid
SEntropy
Temperature (K)0
0
fusion
vaporization
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The Statistics of Entropy
Another way to think about entropy is that being disordered is just more likely.
It’s just chance
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A box containing air molecules, divided in two compartments with a hole in the dividing wall. Since there are many more molecules in the left compartment, there will also be many more molecules crossing the divide from left to right.
The second law of thermodynamics states that in an isolated system the entropy will increase. In the statistical definition of entropy according to Boltzmann, this means that the system will evolve to its most probable state.
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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?
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Entropy, Marble Example, Results
• The most ordered are the least likely• The most disorder is the most likely
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Entropy & Time
Because systems move from order to disorder, time has a direction.
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Which came first?
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Entropy and Life
Life is an entropy reducerDoes this break the second law of thermodynamics?
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