1. The Second Law of Thermodynamics
The Hotter to the Cooler
Standards
3d Students know that most processes tend to decrease the order of a system over time and that energy levels are eventually distributed uniformly.
3e Students know that entropy is a quantity that measures disorder of a system and that this quantity is larger for a more disordered system.
3f* Students know the statement “Entropy tends to increase” is a law of statistical probability that governs all closed systems (second law thermodynamics).
3g* Students know how to solve problems involving heat flow, work, and efficiency in a heat engine and know that all real engines lose some heat to their surroundings.

2. The Second Law of Thermodynamics
In a closed system the following processes tend to occur spontaneously:
Energy tends to move until it is equally spread out throughout the system
Entropy (randomness) tends to increase
Closed system is one in which no objects or energy enters or leaves.
Spontaneous means there is no forcing by some outside mechanism
Statistical law that says what happens most of time NOT what always happens
Questions: What does the second law of thermodynamics say? What is meant by the words spontaneously and closed system? What do we mean when we say that the second law is a statistical law of probability?
Activities:
1) Point out that though we know that heat moves from hot to cold we have no law that states this
2) Write second law out on board prior to lecture and point it out at the beginning
3) Define a closed system
4) Define spontaneous
5) Describe what is meant by the second law being a statistical law of probability

3. Consequences of the Energy version of the 2nd Law
Heat will flow from hot to cold
Things tend to seek position of lowest potential energy (think electrons in atoms and rolling down hill)
More and more easily useful energy is becoming less useful heat that will flow until entire universe is same temperature
Work becomes heat at 100% efficiency which will eventually result in a universe w/ the same temperature throughout and heat death.
Question: What are the consequences of the second law for: a) heat flow b) potential energy of a system or object c) useful energy d) heat e) the universe
Activities:
State that energy version of second law means that heat will flow from hot to cold as this would cause a greater spread of energy throughout a system.
Point out that electrons circling atoms, planets orbiting sun and ball rolling down hill all are examples of decreasing potential energy. Here again we are spreading the energy out from one object to the entire universe.
Discuss how chemical energy in oil, coal and natural gas all is extremely organized and easily usuable. This energy becomes heat when we use it to power our world which is very disorganized and hard to use energy. The energy crises is thus not about losing energy but losing sources of easily usable energy.
Discuss what this law means for the ultimate fate of the universe=>heat death

4. The 2nd Law Applied to a Heat Engine
No engine is 100% efficient
Ecarnot =Thot-Tcold /Thot x 100%
Efficiency increases with higher input tempertures
Efficiency increases with lower output temperatures
Later results in greater increases in efficiency
Work = Qout-Qin
Questions: Can any engine be 100% efficient in changing work to heat? Why not? Write an equation that calculates how efficient a friction free engine can be. What are the two ways to increase the efficiency of an engine? Which gives you a better bang for your buck?
Activities:
1 Draw a heat engine diagramatically on board and remind students how it works.
2 Show transparency of steam engine and talk about back pressure of gas that has gone past a turbine. Say that in general all engines will have some mechanism like this that resist an ever increasing speed.
3 Ask how efficient can such an engine be and write carnot’s equation. Point out two ways that can increase efficiency of engine and that lowering exhaust temperature results in faster increases in efficiency. Cite the tail pipe of a car is used to exhaust heat into the coolest part of a car the outside. Also discuss how fuel efficiency increases during winter.
4 Demo above by cooling smoke stack of small steam engine

5. The Entropy Version of the 2nd Law
Entropy is the measurement of disorder
More disorder means more entropy
The second law says that entropy spontaneously increases w/ time
Gases tend to spread out
Matter tends to mix with other matter
Solids become liquids become gases
All energy will eventually become heat
Questions: Define entropy. Does higher entropy mean more or less disorder? Which of the following conditions for a system has a higher entropy: a) gas at a high versus low temperatures b) gas in a small or large volume c) two types of matter in the same container in a mixed or unmixed state d) matter in solid or liquid form e) matter in liquid versus gaseous form f) energy in the form of chemical bonds or heat?
Activities
1 Define entropy as amount of disorder in system and that more entropy means more disorder.
2 Use examply of 5 year old as a very entropic device. Relate story of Turantulla and dolls, bath tub and water and finally writing a letter to grandma as examples of entropy increasing. Also float building episode.
3 State that other increases in entropy include going from low to high temps, gases spreading out, matter mixing together, solids becoming liquids becoming gases and energy all becoming heat.

6. Apparent Exceptions to the Second Law
Living things organize matter and energy in order to live
Produce heat in order to do this which increases entropy of universe and brings us that much closer to the end
A refrigerator pumps heat out of the inner compartment and dumps it into the hotter atmosphere
This is done by having a pump do work on a gas. This work will eventually become heat along with the heat dumped into the atmosphere and increase the entropy of the universe
Once in a great while things do become more ordered
Second law is a statistical law of probability that tells us what happens most of the time not what always happens
Questions: Explain why the following are not violations of the second law of thermodynamics: a) living things b) a refrigerator c) all the air in a room rushing to one corner.
Activities:
State In general violations of second law cannot occur because no system except the universe is absolutely closed and the law is statistical in nature.
Go through life example
Go through refrigerator or air conditioner example
Point out that both of above systems were not closed
Go through air moving to single corner of room example
Show density bead bottle demo and point out that like the fridge here we also have a forcing mechanism
Repeat that In general violations of second law cannot occur because no system except the universe is absolutely closed and the law is statistical in nature.