1. Ch. 6 – Thermal Energy I. Temperature and Energy Transfer Temperature
Heat Transfer

2. A. Temperature Temperature
measure of the average KE of the particles in a sample of matter
Thermometers rely on expansion

3. B. Temperature Scales Fahrenheit and Celsius most familiar to you
Celsius used often in science – why?
Kelvin, based on Celsius and absolute zero
Absolute zero = temperature at which an object’s energy is the lowest
Celsius – Kelvin Conversion
K = oC + 273
? K = 32oC
K = 32oC = 305K

4. Answers to Homework p. 328 1. a. -423.2 oF 20K b. -40.0 oF 233K
c oF 1337K
2. See table
3. D
4. C Ex oC oF K
LR Air 21 70
294
Metal in car
115
239
388
Liquid N
-200
-328 73
Desert air 43
110
316

5. C. Energy Transfer
Molecules of warmer substance are moving faster than molecules of colder substance
As these substances come in contact with each other, energy is transferred from warm to cold objects because of collisions of particles
Example: ice cube in a warm hand

6. D. Thermal Energy Thermal Energy
the total energy of the particles in a material
KE - movement of particles
PE - forces within or between particles due to position
depends on temperature, mass, and type of substance

7. D. Thermal Energy A B Which beaker of water has more thermal energy?
B - same temperature, more mass
200 mL
80ºC A
400 mL B

8. E. Heat Transfer Heat Like work, heat is...
thermal energy that flows from a warmer material to a cooler material
Like work, heat is...
measured in joules (J)
a transfer of energy

9. A B E. Heat Transfer A B Why does A feel hot and B feel cold? 80ºC
Heat flows from A to your hand = hot
Heat flows from your hand to B = cold
80ºC A
10ºC B A B

10. F. Thermal Energy Transfer
Conduction
Convection
Radiation

11. G. Conduction Conduction = movement of heat energy by direct contact
Good conductors = material through which energy can be easily transferred as heat
Ex: metals, saltwater
Opposite of conductor = insulator – slows the transfer of energy as heat
Ex: cork, wood, glass, air

12. H. Convection
Convection is the movement of gases or liquids from a warmer spot to a cooler spot
A lava lamp displays convection as heated wax expands and rise and cooler wax falls

13. I. Radiation
Electromagnetic waves - require no matter to travel through; ex: light, IR, UV
Electromagnetic waves transfer energy = radiation
When sunlight hits earth, its radiation is absorbed or reflected
Darker surfaces absorb more of the radiation and lighter surfaces reflect the radiation

14. J. Thermal Energy Summary
Room is warmed by radiation

15. K. Heat Transfer Specific Heat (C)
amount of energy required to raise the temp. of 1 kg of material by 1 degree Kelvin
units: J/(kg·K) or J/(kg·°C) or J/(g·°C)

16. K. Heat Transfer 50 g Al 50 g Cu Al – It has a higher specific heat
Which sample will take longer to heat to 100°C?
50 g Al
50 g Cu
Al – It has a higher specific heat
Al will also take longer to cool down

17. q = m  C  T K. Heat Transfer q: heat (J) m: mass (kg)
C: specific heat (J/kg·K)
T: change in temperature (K or °C)
– q = heat loss
+ q = heat gain
T = Tf - Ti

18. K. Heat Transfer heat gained = heat lost Calorimeter
Coffee cup Calorimeter
Calorimeter
device used to measure changes in thermal energy
in an insulated system:
heat gained = heat lost

19. K. Heat Transfer GIVEN: WORK: m = 32.0 g q = m·C·T Ti = 60.0°C
A 32.0-g silver spoon cools from 60.0°C to 20.0°C. How much heat is lost by the spoon?
GIVEN:
m = 32.0 g
Ti = 60.0°C
Tf = 20.0°C
q = ?
C = 235 J/kg·K
WORK:
q = m·C·T
m = 32 g = kg
T = 20°C - 60°C = – 40°C
q = (0.032kg)(-40°C)(235J/kg·K)
q = – 301 J

20. K. Heat Transfer GIVEN: WORK: m = 230. g q = m·C·T Ti = 12.0°C
How much heat is required to warm 230 g of water from 12.0°C to 90.0°C?
GIVEN:
m = 230. g
Ti = 12.0°C
Tf = 90.0°C
q = ?
C= 4184 J/kg·K
WORK:
q = m·C·T
m = 230 g = 0.23 kg
T = 90°C - 12°C = 78°C
q = (0.23kg)(78°C)(4184 J/kg·K)
q = 75,000J

21. K. Heat Transfer GIVEN: WORK: m = .400 kg q = m•C•T Ti = 273 K
A kg sample of glass requires 3190 J for its temperature to increase from 273 K to 308 K. What is the specific heat for this type of glass?
GIVEN:
m = .400 kg
Ti = 273 K
Tf = 308 K
q = 3190 J
C= ? J/kg·K
WORK:
q = m•C•T
T = 308 K – 273 K = 35 K
(3190 J) = (0.400 kg)(35 K)C
C= 228 J/kg·K

22. K. Heat Transfer GIVEN: WORK: m = 550 g q = m·T·Cp Ti = 24°C
CCu= 0.38 J/g·K
How much energy would be absorbed by 550 g of copper when it is heated from 24°C to 45°C?
GIVEN:
m = 550 g
Ti = 24°C
Tf = 45°C
q = ?
C= 0.38 J/g·K
WORK:
q = m·T·Cp
T = 45°C - 24°C = 21°C
q = (550g)(21°C)(0.38 J/g·K)
q = 4,400 J

23. Assignments
Homework
Finish Thermal Energy WS – Work on it now so you can get some help!

24. Using Heat
Cooling buildings, heating homes, preserving food is all because of heat transfer
First Law of Thermodynamics – energy is conversed when transferred to due to work, heat or both
Second Law of Thermodynamics – energy transferred always moves from high temp object to low temp object

25. Cooling Systems
Substances that easily evaporate and condense are used in air conditioners
When liquid evaporates, absorbs energy from surrounding air, cooling it
Outside, gas condenses, releasing energy