1. * Thermal Energy Temperature Heat Transfer
07/16/96
Temperature and Heat
Thermal Energy
Temperature
Heat Transfer *

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

3. Thermal Energy Thermal Energy
the total energy of the particles in a material
KE - movement of particles (faster=more KE)
PE - forces within or between particles due to position
The sum of the kinetic and potential energy of all the particles in an object is the thermal energy of the object.
depends on temperature, mass, and type of substance

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

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

6. 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

7. a. The flow of thermal energy from one object to another.
Cup gets cooler while hand gets warmer
Heat
a. The flow of thermal energy from one object to another.
b. Heat always flows from warmer to cooler objects.
Ice gets warmer while hand gets cooler

8. Heat Transfer C 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)

9. 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.

10. Q = m  T  Cp 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

11. Heat Transfer heat gained = heat lost in an insulated system,
Calorimeter
device used to measure changes in thermal energy
in an insulated system,
heat gained = heat lost

12. 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

13. 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