1. Thermal Energy and Heat
Chapter 14

2. Section 1: Temperature, Thermal Energy, and Heat

3. Temperature
A measure of the average kinetic energy of the individual particles in matter.
The faster the particles move, the more kinetic energy.
We use a thermometer to measure temperature.
3 Scales: Celsius, Fahrenheit, Kelvin

4. Celsius scale
Boiling point of water = 100˚C
Freezing point of water = 0˚C
Fahrenheit scale
Boiling point of water = 212˚F
Freezing point of water = 32˚F
Kelvin scale
Boiling point of water = 373K
Freezing point of water = 273K

5. ˚C = K - 273
K = C formulas
Convert 303K to ˚C
303K – 273 = 30˚C
Convert 70˚C to K 70˚C = 343K
absolute zero = 0K or -273 ˚ C
At absolute zero, there is no kinetic energy in the particles / no thermal energy can be removed

6. Thermal Energy and Heat
Thermal Energy depends upon:
1. the number of particles in the object
2. the temperature of the object
3. the arrangement of the particles
Heat is:
thermal energy which moves from a warmer object to a less warm object.
Example-ice cube melting in your hand

7. Examine the beakers below.
Which beaker holds more water molecules?
Which beaker has a higher temperature?
Which beaker has more kinetic energy?
Which beaker has more thermal energy?
Which beaker has the greatest mass?

8. Specific Heat
The amount of energy required to raise the temperature of one kilogram of a material by one Kelvin.
Unit for specific heat: J/(kg*K) Formula:
change in energy = mass x specific heat x change in temperature
Material with a high specific heat can absorb a lot of thermal energy without a great change in temperature.

9. Materials with a low specific heat will absorb heat quickly and easily.
Ex: Sand on the beach
Ex: gold (bracelet)
Ex: concrete/pavement/tar
Ex: iron
Ex: copper
Ex: silver

10. Sample Problem
How much heat energy is required to raise the temperature of 5kg of water by 10 Kelvins?
Given information:
mass = 5kg
change in temp (∆T) = 10K
specific heat of water = 4180J/(kg*K)
Unknown: change in energy

11. 3 Steps to Solve This Problem
Formula:
change in energy = mass x specific heat x ∆T
Substitution:
energy = 5kg x 4180J/(kg*K) x 10K
Answer:
20,900 J

12. Section 2: The Transfer of Heat

13. How is Heat Transferred?
3 ways that heat can move:
1. Conduction
2. Convection
3. Radiation

14. Conduction Heat is transferred by the direct contact of particles
Example: the heat energy from the hot soup is transferred by conduction to the spoon—the spoon then becomes warm.

15. Convection
Heat is transferred by the movement of currents within a fluid (liquid or a gas)
Example: boiling water—water is moved by the currents in the fluid
When fluids are heated, the particles move faster and further apart.
Pizza oven
Opening an oven and feeling a blast of hot air

16. When fluids are heated, they rise upward because they become less dense
Example: hot water/air rises and cool water/air sinks
The rise and fall of these fluids create convection currents (circular motion)

17. Radiation The transfer of heat energy by electromagnetic waves
Example: fire, sun’s energy
Does not require matter to transfer thermal energy

18. Heat Moves One Way
Heat will always flow from a warmer object to a cooler object.
As thermal energy increases, the temperature of matter absorbing the heat increases.
The temperature of the matter losing the thermal energy is dropping.
Note: there is no such thing as “coldness”

19. Conductors and Insulators
Conductor: material that transfers thermal energy well
metal spoon
most metals
Insulator: material that does not transfer thermal energy well
wood
wool
straw
goose feathers/down comforter
insulation

20. Section 3: Thermal Energy and States of Matter

21. States of Matter
Solid
Particles are packed tightly together
Particles only vibrate
Retain their shape and volume

22. Liquid
particles are close together
particles are free to move around
does not have a definite shape
has a definite volume

23. Gas
particles are moving very fast!
particles are spread very far apart
gases expand to fill available space
lack a fixed shape and volume

24. Changes of State
Change of State: physical change of matter from one state of matter to another (occurs when heat energy is absorbed or released)
Solid-Liquid Changes:
1. melting: solid changes to a liquid
2. freezing: liquid changes to a solid

25. Liquid-Gas Changes:
Vaporization: change from a liquid to a gas (absorbs heat energy)
1. evaporation: vaporization that takes place at the surface of a liquid
2. boiling: vaporization that takes place below the surface of a liquid
3. condensation: a change from a gas to a liquid (cold drink in the summer-loses heat energy)

27. Thermal Expansion
As the thermal energy of matter increases, its particles spread out and the substance expands.
The expansion of matter when it is heated is thermal expansion.
Example: metal grooves on a bridge