1. Ch. 5 - Energy II. Thermal Energy (p.134-137, 141-144) Temperature
Heat Transfer

2. A. Temperature Temperature
measure of the average KE of the particles in a sample of matter

3. Measuring Temperature
A thermometer is a instrument for measuring temperature.
Uses a standard for comparison.
Examples: Celsius, Fahrenheit, and Kelvin Scales

4. Celsius Scale (oC)
Based on freezing point (0oC) and boiling point (100oC) of water
Standard metric scale for measuring particle temperature

5. Kelvin Scale (K) Using absolute zero as a standard
Absolute zero is the temp. where kinetic molecular motion stops
Conversion: ( oC)= Kelvin

6. Temperature vs. Heat Temperature:
A measure of average kinetic energy of an object
Use standard scales: (K), (oC)
Temp. is not a measure of the total amount of energy in an object

7. Temp. vs. Heat Heat: Energy given off or absorbed by an object
Measures the motion of molecules in an object
Measured in Calories

8. B. 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

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

10. Thermal Energy Cont. Total energy of the particles in a material
A sum of both kinetic and potential energy
A more massive object has more thermal energy at the same temperature than a less massive object.

11. C. Heat Transfer
Heat
thermal energy that flows from a warmer material to a cooler material
Like work W=F x d, heat is...
S.I. unit is Calories
Often measured in joules (J)
a transfer of energy

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

13. C. Heat Transfer Specific Heat (Cp)
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)

14. Specific Heat Cont.
The ability of a substance to absorb heat energy (specific heat)
Different substances absorb heat at different rates (land versus water)
The greater the mass of an object the more heat it absorbs

15. C. Heat Transfer 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.

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

17. C. 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

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

19. C. Heat Transfer GIVEN: WORK: m = 230 g Q = m·T·Cp Ti = 12°C
How much heat is required to warm 230 g of water from 12°C to 90°C?
GIVEN:
m = 230 g
Ti = 12°C
Tf = 90°C
Q = ?
Cp= 4184 J/kg·K
WORK:
Q = m·T·Cp
m = 230 g = 0.23 kg
T = 90°C - 12°C = 78°C
Q = (0.23kg)(78°C)(4184 J/kg·K)
Q = 75,061 J

20. Forms of Heat Transfer Three forms of Heat Transfer:
(6.1- pgs )
Conduction
Convection
Radiation

21. Conduction
Conduction involves the transfer of heat through direct contact
Heat conductors conduct heat well, insulators do not

22. Takes place in liquids and gases as molecules move in currents
Convection
Takes place in liquids and gases as molecules move in currents
Heat rises and cold settles to the bottom
Creates weather patterns and ocean currents

23. Fluid Convection
Currents are formed be the movement of liquids and gases from warmer to cooler areas.

24. Radiation Heat transferred through space
Energy from the sun being transferred to the Earth

25. Thermal Pollution (5.3- 138-140)
Occurs when waste heat significantly changes the temperature of an environment
Warmed water from factories decreases dissolved oxygen in water