COP Refrigerators and Heat
Pumps
Reverse World
http://www.youtube.com/watch?v=EahHTh
BjDB0
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
𝑠 = 𝑘𝐵 ln(𝑤)

– Quantization

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.
B.
Reversible
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
scrambling eggs
eating fish
reversible
ice  liquid at 0oC
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
dQreversible
S  
T
i
Ice Melting
Isothermal Expansion
Which path has a larger ∆S
P
A
B
V
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. True
B. False
Non-reversible ideal gas process
Any path will do.
Pick one you can calculate!
S  ncV ln
Tf
Ti
 nR ln
Vf
Vi
If an ideal gas undergoes a nonreversible process, which of the
following will be true?
A.
B.
C.
D.
The entropy will increase
The entropy will decrease
The entropy will stay the same
It depends
Free expansion
The change in entropy for a free expansion
is
a) Positive
b) Negative
c) Zero
d) I do not know
Free expansion
Free expansion followed by
isothermal compression
Conduction
HOT
COLD
Ordered
WARM
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