1. Chapter 14
Heat and Temperature

2. Intro: Discussion
A person from Seattle tells his friend from Florida that the weather in Seattle is somewhat warm. When the friend arrives for a visit, he finds that he is uncomfortably cool wearing the shorts he packed. What would be a more effective way for the person from Seattle to explain the weather?

3. Temperature So, what kind of energy does temperature measure?
The degree of “hotness” or “coldness” of an object,
related to the average kinetic energy of an object’s atoms or molecules
What makes something hot?
Particles that make up matter are in constant motion
They have kinetic energy
When you heat something the particles move faster
So, what kind of energy does temperature measure?

4. Kinetic Energy Kinetic Energy Temperature
transferred as particles collide
Particles are always in motion no matter what state they are in.
What is happening to the coffee?
What else is being affected?
Kinetic Energy
Temperature

5. Measuring Temperature
Thermometers- mechanical or electrical device for measuring temperature.
How thermometer works:
Most materials expand when heated.
Liquid thermometers have a large bulb hooked to a narrow tube.
When the liquid expands it rises up the tube.
Won’t work if too hot or cold

6. Measuring Temperature
Metals expand when heated
Different metals expand different amounts
Hook two metals together to make a thermometer that turns
Bimetallic Thermometers
Used in thermostats
Iron
Copper
Cold
Hot

7. Limits of Temperature Upper Limit No upper limit exists.
Plasma found in starts= millions of degrees C
Lower Limit
Definite limit called absolute zero.
Molecules will slow down SO much, they will essentially stop moving
Out of energy, so they can’t get any colder.

8. Temperature Scales Three different scales:
1. Fahrenheit- the one we use
2. Celsius- metric standard
3. Kelvin- starts at absolute zero but same degree size as Celsius
Fahrenheit scale.
In the US we know at 32 ⁰F water freezes and 212 ⁰F water boils.

9. Measuring Temperature
The absolute temperature scale is called the Kelvin scale.
Absolute zero is 0 K.
The melting point of ice is 273 K, and the boiling point of water is 373 K.
There are no negative numbers on the Kelvin scale.

10. 0⁰C
32⁰F
273 K

11. 100⁰C
212⁰F
373 K
0⁰C
32⁰F
273 K

12. 100⁰C
212⁰F
373 K
0⁰C
32⁰F
273 K
-273⁰C
-492⁰F
0 K
Notice anything else about the scales?

14. Heat
We know that temperature is the hot or cold nature of something (based on the kinetic energy of its molecules),
So what is heat?
Heat is the thermal energy transferred from one thing to another due to a temperature difference.
Always moves from high temperature to low temperature.
Faster molecules (high temperature) hit slower molecules (low temperature) and speed them up

15. Heat Temperature tells you direction of heat transferring.
If you touch a hot stove, thermal energy enters your hand because the stove is warmer than your hand. When you touch a piece of ice, thermal energy passes out of your hand and into the colder ice.
Temperature tells you direction of heat transferring.

16. 14.2 Energy Transfer Heat can be transferred 3 different ways:
Conduction
Convection
Radiation

17. Energy Transfer: Conduction
Transferred of energy by direct contact
Works well in some solids, then liquids, and least in gases.
Conductors- materials that allow heat to pass through them
Most metals
Insulators- materials that don’t let heat pass through them well
Rubber, plastics, glass, air

18. Energy Transfer: Convection
Transferring energy by moving fluids
Liquids and gases are fluids
When heated they expand, become less dense
They rise, replaced by cooler denser fluids
Make a circular flow called a convection current
Clip

19. Water movement Cools at the surface Convection current Hot water rises
Cooler water sinks

20. Why is it windy at the seaside?

21. Energy Transfer: Radiation
Energy transferred by electromagnetic waves
Ex: infrared radiation, visible light, ultraviolet rays
Can travel through empty space
When wave hit object they make the molecules move faster.

22. Emission experiment
Four containers were filled with warm water. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its shiny surface reflects heat _______ back into the container so less is lost. The ________ container would be the coolest because it is the best at _______ heat radiation.
shiny metal
radiation
dull black
emitting

23. Absorption experiment
Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes?
Shiny metal
Dull metal
Dull black
Shiny black
The __________ container would be the warmest after ten minutes because its surface absorbs heat _______ the best. The _________ container would be the coolest because it is the poorest at __________ heat radiation.
dull black
radiation
shiny metal
absorbing

24. Specific Heat Some materials heat up easily
Others require a large amount of energy to change their temperature
Specific heat measures the amount of energy required to raise the temperature 1 kg of a substance by 1 degree Kelvin
Table on page 485 (Learn to use it)
Water has a high specific heat of 4186 J/kg K

25. Specific Heat
The amount of energy required to change the temperature of substance identifies type of conductor.
Metals have a low specific heat

26. Calculating Specific Heat
Energy = Specific heat x mass x change in temp
Energy (Q) = cmDT
mass= kg
energy= Joules
Temperature= K
c= specific heat Q c m DT
Specific heat is the “price” to change 1 kg of a substance.

27. Practice Problems: Specific Heat
1. How much energy must be transferred as heat to 200 kg of water in a bathtub to raise the water’s temperature from 25 °C to 37 °C?
energy = 4186 x 200 kg x 12 k
energy = cmDT
DT= 37 °C- 25 °C
DT= 12 K
energy = 10,000,000 J or 1.0 x 107 J
m= 200 kg
c= 4,186 J/kg x K
energy = ?

28. Practice Problems: Specific Heat
2. How much heat does it take to change the temperature of 3 kg of water by 75 K?
energy = cmDT
energy = 4186 x 3 kg x 75 k
DT= 75 K
energy = J or 9.0 x 105 J
m= 3 kg
c= 4,186 J/kg x K
energy = ?

29. Practice Problems: Specific Heat
3. How much energy is needed to increase the temperature of kg of iron from 283 K to 403 K?
energy = 449 x kg x 120 k
energy = cmDT
energy = 40,700 J
DT= 403 K -283 K
DT= 120 K
m= kg
c= 449 J/kg x K
energy = ?

30. 1st Law of Thermodynamics
The word thermodynamics stems from Greek for “movement of heat.”
First Law of Thermodynamics:
When thermal energy transfers as heat, it does so without net loss or gain. The energy lost from one place is gained by the other.
Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. (You can’t get something from nothing because energy and matter are always conserved).

31. 2nd Law of Thermodynamics
Energy transfers as heat always moves from a hot to cold objects. (You can’t break even; you can’t return to the same energy state because entropy always increases).
Entropy is the tendency for natural systems to become disorganized over time.
Any system that is left to itself will fall apart. This means Entropy increases.
Usable energy decreases with every transfer or energy transformation.

32. Thermodynamics Work increases average kinetic energy
Mechanical Process is the process in which energy is transferred by work.
Bow drill

33. Heat Engines
Heat engines convert chemical energy to mechanical energy through the process of combustion.
Internal combustion engines
Fuel burns inside the engine
A carburetor is the part of the engine in which liquid gasoline becomes vaporized.
4 strokes: Intake, Compression, Power, and exhaust
Automobile Cylinder Animation

34. Chapter 3.2 Changes of State
What happens when a substance changes from one state of matter to another?
What happens to mass and energy during physical and chemical changes?

35. Temperature vs. Time
Adding energy either raises T or changes state, not both at the same time.

36. Energy and Changes of State
The identity of a substance does not change during a change in state
The ability to change or move matter
As you add energy to a liquid, the temperature goes up separating molecules
Some changes of state require energy
Melting, evaporation and sublimation
melting
sublimation
evaporation

37. Energy and Changes of State
Evaporation
The change of state from a liquid to a gas
Boiling Point- The temperature at which a liquid boils.

38. The temp in the room is about 22°C and 70°F.
The temperature of boiling water is 100oC on the celsius scale and 212oF on the Fahrenheit scale.
The temp in the room is about 22°C and 70°F.
Are the following temperatures hot or cold?
65°F

39. Sublimation The process in which a solid changes directly into a gas
Ex. Dry ice (Carbon dioxide in the solid form) changes directly from a solid to a gas
Video Clip

40. Melting Point
The temperature at which a substances changes from solid to liquid.
Melting point depends on the pressure.
32 degrees F
0 degrees C

41. Energy is released in some changes of state
Freezing and condensation
Freezing
Condensation

42. Solid Liquid Gas sublimation Freezing Condensation Melting
Boiling or evaporation
Solid
Liquid
Gas
Freezing
Condensation

44. Temperature
The temperature of a substance does not change during a change of state.
For example, if you add energy to ice at 0oC, the temperature will NOT rise until all of the ice has melted.