COP Refrigerators and Heat Pumps

Reverse World BjDB0 BjDB0

Test 2 Starts Friday Oct 18 Starts Friday Oct 18 Ends Monday Oct 21 Ends Monday Oct 21 Late day Tuesday Oct 22 Late day Tuesday Oct Multiple Choice 16 Multiple Choice 4 Free Response 4 Free Response Give yourself plenty of time! Give yourself plenty of time!

Entropy is a measure of disorder… But what does that mean? 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) Information (compression) Parking a Car Parking a Car Clutter Clutter Thermodynamic Thermodynamic –Quantization

Reversible vs. Irreversible Irreversible Irreversible –Free expansion (adiabatic-ish) –Heat conduction –Scrambling Eggs, Bar room fight Reversible Reversible –Adiabatic expansion –Constant T expansion (at least for the gas) –Ice melting (sort of) Isolated vs Open Systems Isolated vs Open Systems

Water runs over a waterfall. What kind of process is this? A. Reversible B. Irreversible

Reversible process - one that works equally well in reverse, one whose effect you can undo 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 Irreversible process - one you cannot undo or will not spontaneously run in reverse Pretty much all spontaneous events in nature are irreversible Pretty much all spontaneous events in nature are irreversible irreversiblereversible irreversiblereversible scrambling eggsice  liquid at 0 o C scrambling eggsice  liquid at 0 o C eating fish eating fish liquid  steam at 100 o C liquid  steam at 100 o C

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.

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

Ice Melting

Isothermal Expansion

Which path has a larger ∆S 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. True B. False

Non-reversible ideal gas process 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 increase B. The entropy will decrease C. The entropy will stay the same D. 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 HOTCOLD 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