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COP Refrigerators and Heat Pumps
Reverse World
http://www.youtube.com/watch?v=EahHThBjDB0
Test 2 Starts Friday Oct 18 Ends Monday Oct 21 Late day Tuesday Oct 22
16 Multiple Choice 4 Free Response Give yourself plenty of time!
Entropy is a measure of disorder…
But what does that mean?
Micro vs Macro States
Entropy is about probability.It is very improbable that we will ever observe a process
that decreases the entropy of a real physical process.
In the limit as N goes to infinity, probability becomes
fact.Consider the air in this room.
Entropy – it’s different things to different people
Information (compression) Parking a Car Clutter Thermodynamic
– Quantization
𝑠=𝑘𝐵 ln (𝑤)
Reversible vs. Irreversible Irreversible
– Free expansion (adiabatic-ish)– Heat conduction– Scrambling Eggs, Bar room fight
Reversible– Adiabatic expansion– Constant T expansion (at least for the
gas)– Ice melting (sort of)
Isolated vs Open Systems
Water runs over a waterfall. What kind of process is this?
A. ReversibleB. Irreversible
Reversible process - one that works equally well in reverse, one whose effect you can undo
Irreversible process - one you cannot undo or will not spontaneously run in reverse
Pretty much all spontaneous events in nature are irreversible
irreversible reversible scrambling eggs ice liquid at 0oC eating fish
liquid steam at 100oC
Puff Balls
Law of Increasing Disorder (2nd Law of Thermodynamics)
Changes occurring in natural systems always proceed in such a way that the total amount of disorder in a closed system never decreases, and it increases in irreversible processes.
http://www.youtube.com/watch?v=X4zd4Qpsbs8&NR=1
2 Ne 9:28
O that cunning plan of the evil one! O the vainness, and the frailties, and the foolishness of men! When they are learned they think they are wise, and they hearken not unto the counsel of God, for they set it aside, supposing they know of themselves, wherefore, their wisdom is foolishness and it profiteth them not. And they shall perish.
Increase in Entropy = Increase in disorder
f
i
reversible
T
dQS
Ice Melting
Isothermal Expansion
Which path has a larger ∆SP
V
B
A
C. The same
D. Not enough information
Quick Quiz 22.6 The entropy change in a free expansion must be zero
because Q=0
A. TrueB. False
Non-reversible ideal gas process
i
f
i
fV V
VnR
T
TncS lnln
Any path will do.Pick one you can calculate!
If an ideal gas undergoes a non-reversible process, which of the
following will be true?
A. The entropy will increaseB. The entropy will decreaseC. The entropy will stay the sameD. It depends
Free expansion
The change in entropy for a free expansion is
a)Positiveb)Negativec)Zerod)I do not know
Free expansion
Free expansion followed by isothermal compression
Conduction
HOT COLD
WARM
Ordered
Disordered
Universal Heat Death
“This is the way the world ends, not with a bang but a whimper.”
T.S. Eliot
Gospel perspective
"every thing restored to its perfect frame"
Alma 11:44