1. Chapter 9 Heat

2. What is hot?
1700s - Caloric – heat fluid that flows from hot to cold items till equal in each
Fails to explain rubbing hands together
Old school theory

3. What is hot?
Today – Kinetic-Molecular theory – atoms or molecules are constantly in motion, the faster they move the hotter the body (more and high velocity collisions)
How hot something is depends on the average KE of its particles
Remember chemistry?

4. Internal Energy
Energy of the particles’ motion is called Internal Energy (symbol U)
Several types of particle motion energy
Translational – (measured by temp)
Rotational
Vibrational

5. Energy flow between objects
Energy flows between objects by collisions – fast ‘hot’ particles transfer momentum & energy to slow ‘cold’ particles

6. Thermal Equilibrium
When both objects have same avg. KE (temp) then energy is flowing equally in both directions
To get a temperature – must get thermal equilibrium between object & thermometer
Demonstrate equlibrium, not no flow, equal flow. Pour water back and forth between two cups
Therm-o-meter – needs thermal equilibrium to work, not instant when you put it in something

7. Thermal Expansion Objects expand when their temperature increases*
We can calculate rate of expansion per degree temperature for different materials
How Thermometers Work

8. Temperature Scales Fahrenheit – 1720s thermometer maker Celsius - 1742
Standard cold temp – salt water freezing
Water freezes: 32° Water Boils: 212°
Celsius
Based on water
Water freezes: 0° Water Boils: 100°
Kelvin
Starts at coldest possible temperature Water freezes: Water Boils:

9. High Quality H2O Water boils at Water Freezes at 100oC 212oF 373 K 0oC
Need to memorize these 6 values – then can convert anything

10. Absolutely Cool Absolute Zero
Temperature at which KE is no longer present
0 K = oC
Unreachable – Measuring temperature adds KE (thermal equilibrium with thermometer)
Then how do we know it is the coolest?
Do absolute zero graphing activity

11. Is It Getting Hot in Here
Matter contains energy, not heat
Paperclips
HEAT is : Energy that is transferred from high temperature substances to low temperature substances
Hand out paperclips – twist back & forth till it breaks – hold end – its hot!
KNOW THIS DEFINITION!!!!
Like water flowing downhill – energy flows from hot to cold

12. Heat
Heat’s symbol is Q
measured in Joules or calories or BTUs or kilocalories or Calories or Therms
James Joule showed equivalence between thermal and mechanical energy - diagram

13. How does it flow Thermal Energy moves from high to low temperature
Particle collisions transfer translational KE
Rate directly proportional to Temperature difference
Newton’s law of cooling R ~ ΔT
Newton’s law of cooling

14. Too Hot to Handle Thermal Energy Transferred in 3 ways Conduction
Convection
Radiation
Ask them if they know the 3 ways first…

15. Conducting Business Conduction
Heat transferred through CONTACT – atoms of one material crash into atoms of other material
Conductors are good at it
Insulators are bad at it
What is heat? What is temperature? Conduction is atoms crashing – momentum being transferred
Do desk example – touch metal, touch top
Show Hewitt videos – air is insulator and walking on hot coals
Styrofoam, down jackets, house insulation, double pane windows, metal vs. plastic windows, vacuum bottles

16. Convection Convection Transfer of energy through fluids
Not so much energy transfer as matter transfer
Archimedes’ principle applied
Convection currents produce winds
Show Eureka Video – Show example on the board – lake wind examples – boiling water example – Sun example
Works in all fluids!

17. Full of Cold Air Air is cooler at higher altitudes
Less pressure so: gases are able to expand
Lower density = less kinetic energy
Air is very low altitudes
This is why it is cold at higher altitudes – cold in Denver, on Everest, warm in Death valley & Jordan Valley
Death Valley

18. You’re So Radiant Forms of radiant energy
Microwaves UV IR
Radio
Visible
Gamma
Heat transfer from sun is radiation
Energy transmitted via radiation is radiant energy
Doesn’t have to be touching, doesn’t need air or fluid – only way energy can enter from outside the planet

19. Riding the Waves Good absorbers = Good Emitters
Low temperature emit long wavelengths
High temperature emit short wavelengths
We absorb IR waves (heat lamp)
Remember Movie at start of semester – this is black body radiation!!! Only depends on temperature
Heat lamp – absorb & emit IR waves

20. Radiant Energy Absorbing and Reflecting are opposites
Light colors reflect:
radiant energy
All wavelengths
Dark colors absorb:
Silver coffee & drink pitchers, black clothing, white clothing
Coffee/Cream NTQ

21. Energy Conservation Energy still conserved ΔPE + ΔKE + ΔU = 0
Q (heat) is part of the U (internal energy)

22. How much heat?
Materials require different amounts of heat to increase their temperature
Specific Heat (C)– amount of energy needed to raise temperature of 1 kg of material 1 Kelvin
Chart pg 314 for common materials

23. Heat equation Specific heat – math definition
(C)= Heat (Q)/(mass*ΔTemp)
Solve for the heat (Q) needed:
Q = mCΔT

24. Practice with Heat
How much energy is needed to increase the temperature of 45 grams of Silver 25 Kelvin?
If 1.5 kg of water starts at 274 Kelvin, what temperature will it be at if 35,000 Joules of energy are added?

25. Calorimetry – Finding Specific Heat
Energy conservation says the total energy must remain the same. If we isolate a hot object with a cold one, we can be sure all the energy flows to the cold from the hot. If we know the ΔT of each and the Specific Heat of one, we can find the specific heat of the other.

26. Practice Calorimetry
A 1.2 kg mass of unknown metal cools from 115°C to 27°C in 600. ml of water that started at 22°C. What is the specific heat of the metal?
A 2.0 kg block of copper metal that is 125°C is put in 550 ml of 22°C water. What is the final temperature of the water and copper?

27. Water Water Everywhere
Water has a very high specific heat capacity
Advantages
Useful for cooling
Useful for warming
Holds a lot of energy in its temperature
U of I – chilled water cooling – send cold water out in summer – heat of air absorbed into it
Hot water heat – same idea – opposite direction – house I grew up in – this building – hot water bottle in bed
Cars use ‘coolent’ to remove heat from the engine – basically water- talk about anti-freeze later

28. Controlling world climates
Deserts
Why are summer & winter late?
Why do people want to live in California?
Deserts – hot during day – night – sand has low capacity – water high
Thermal Lag – water on earth takes time to warm up/cool down – swim in August, not June, cold in February, not December
Live by a big ocean – California & Florida & England mild – Middle of Continent is hot & cold – kansas – cooler by the lake - Chicago

29. Let’s Expand Our Horizons
Most matter expands when heated
Gases fastest, then Liquids then Solids
Hot-air balloons
Ring & Sphere demo
Bi-metal strip
Thermal rate of expansion
Hot air balloons – air spreads out, less dense – weight is less – buoyancy overcomes
Bi-metal strip – different things different coefficents of expansion

30. Expansion examples How thermostats work Railroads, power lines
Bridge joints
Thermal pipe joints
Show example of thermostat – basically long piece of metal
Why railroads are built like they are – click-clack

31. Exceptions to the Rule Water is different from other substances
Water expands when temperature is above or below 4oC
Water is smallest and most dense at 4oC
This is why Ice floats – draw graph of density vs. Temperature -

32. Phase Transitions
Material changes phase, energy change comes from other internal energy, not KE translational….
so NO TEMPERATURE CHANGE
Latent heat (L) – energy transferred during phase change (Joules/kg)
Q = mL (heat = mass*latent heat)

33. Solid – Liquid transition
Melting/freezing point – temperature at which the transition occurs
Latent Heat of Fusion (Lf)– energy required to melt a solid into liquid –
Also energy given off when liquid freezes to solid

34. Liquid-Gas transition
Boiling/condensing point – temperature at which the transition occurs
Latent Heat of Vaporization (Lv)– energy required to vaporize a liquid into gas
Also energy given off when gas condenses to liquid

35. Water transitions Lf = 3.33*105 Joules/Kg Lv = 2.26*106 Joules/Kg
Chart pg 318 for more common substances
Graph of Water transitions

36. Transition problems
How much energy is needed to convert 1.5 liters of 273 K ice to 273 K water?
How much energy is needed to heat 2.5 kg of 350 K water into 373 K steam?

37. More transition problems
How much water at 360 K could be turned into steam with 25,000 Joules of energy?
How much energy is released as .5 kg of 373 K steam is cooled and frozen into 273 K ice?
What energy is required to turn a 5.0 kg block of ice at -10°C into 110°C steam?

38. It’s Time to Chill Out Freezing Freezing temperature can be altered
Change from a liquid to a solid state
Freezing temperature can be altered
Change in pressure
Adding salt or sugar

39. You’re Getting Warmer Boiling Changing from liquid to gas
Occurs beneath the surface
Cooling process - molecules having the highest KE escape

40. Boiling Dependent on temperature and pressure
Pressure of vapor within the bubbles > pressure of surrounding liquid
Temperatures below boiling point, vapor pressure is not great enough

41. Boiling Higher Atmospheric Pressure Increases Boiling Point
molecules are required to move faster to exert increased pressure within the bubble

42. Boiling Lower Pressure (high altitudes), Decreases boiling point
Pressure Cooker
Vapor builds up inside sealed cooker
Pressure on the surface is increased
Raises boiling point
Increased Temp. cooks the food

43. 2 Phases for the price of 1
Boiling and Freezing can occur at the same time
Regelation
Melting takes place under pressure
Freezing occurs when pressure is reduced

44. Triple Point – all 3 phases @ once