1. Chapter 10 - Thermodynamics
‘heat’-‘movement’

2. Internal Energy
Two main processes can change Internal Energy (U) of a given system
Heat (Q) can flow in or out of system
Work (W) can be done by the system*

3. Life is complicated
System – Set of objects that we define as a distinct group
Environment – everything outside of system
Heat flows from one to other, work is done by one on the other

4. Work by a system
Gases do work by increasing in volume – (internal combustion engines)
W=Fd, ΔV=Ad -> algebra ->
Work = Pressure*ΔVolume
W = PΔV

5. Laws of Thermodynamics
1st Law – Total increase of thermal energy of a system is the sum of the heat added and work done to the system
ΔEnergyinternal = Heat – Work
ΔU = Q – W SIGNS!!!

6. Special cases
Isovolumetric – volume doesn’t change – no work done by or on
Isothermal – no temperature change – internal energy doesn’t change
Adiabatic – no heat flow in or out

7. Laws of Thermodynamics
ΔU = Q – W
Revisit Isovolumetric, Isothermal, Adiabatic, Isolated systems
Chart Page 344

8. Applications of 1st law
Cyclic Processes – back where you started at the end
Heat engines – turn thermal energy into mechanical energy (do work with heat) W = Qh-Qc
Must have a high temperature source and a ‘cold’ heat sink

9. Evaporation Evaporation is Phase change from liquid to gas
Takes place at the surface of the liquid (hot particles leave; cool ones are left behind)
A cooling process
How do you cool your body?
How do you stay cool at Six Flags?
How do you cool a hot cup of coffee?
Energy money game, all start with 4, then play rock, paper, scissors with each other. Winner takes a energy unit. When you reach 6 – go to evaporation land. What is left? THE HOT ONES LEAVE

10. Condensation Condensation is Phase change from gas to liquid
loss of energy due to collision
loss of energy due to attractive forces
A warming process
Why do you feel extra warm on a muggy day?

11. Evaporation>Condensation-cooling
The Going Rate
Evaporation and Condensation take place at the same time
Evaporation>Condensation-cooling
Evaporation<Condensation-warming
Evaporation=Condensation-equilibrium

12. The Going Rate
What can you conclude about a dish of water on a table for several days that has no change in the water level?
Why do you feel chilly after emerging from a shower?
Why do you not feel as chilly if you stay in the shower to dry off?
Dogs, pigs, etc

13. There’s Something in the Air
Saturation of air must occur for condensation to be present
When slow moving molecules collide, they stick together (at higher speeds, they can bounce apart)
Cloud formation attributed to condensation
warm air rises = expands = cools = molecules stick together = condensation upon molecules/ions
Fog - a cloud that forms near the ground

14. Evaporation/Condensation
Human, dog cooling – AZ vs. St. L.
Shower examples
Cloud formation
Fog
Adiabatic example – cold cans & blowing air

15. HSW - Refrigerator Changing pressure to move energy with vapor points
Compressor
Inside coils
Outside coils
Expansion valve
Step by step through the loop with number examples
500 calories of heat absorbed from food to vaporize cool liquid
Compress the gas to raise vaporization temperature (do 100 calories of work)
Compressed gas condenses – releasing 600 calories of energy
Liquid’s pressure is reduced by expansion valve – start over
500 calories out of the fridge – 600 calories released outside
Page

16. How Refrigerators work

17. Efficiency of engines
Efficiency – useful work out of total energy given
Eff. = Wnet/Qh
Eff. = (Qh – Qc)/Qh
Eff. = 1 – Qc/Qh
Chart on page 353

18. Laws of Thermodynamics
Entropy – disorder of system
hotter – faster moving molecules; less entropy (ability to do more work)
cooler – slower moving molecules; more entropy (ability to do less work)
2nd Law – natural processes go in a direction that increases the total entropy of the universe

19. 2nd Law Examples Diffusion of liquids/gases
Heat always flows from hot to cold
Universe ends up cold and dark (all microwaves)
Evolution?

20. THE BIG QUESTION!
Which freezes faster – hot water or cold water? ??