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Ch. 5 - Energy. II. Thermal Energy (p.134-137, 141-144) Temperature Thermal Energy Heat Transfer. A. Temperature. Temperature measure of the average KE of the particles in a sample of matter. B. Thermal Energy. Thermal Energy the total energy of the particles in a material

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Ch. 5 - Energy


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ch 5 energy

Ch. 5 - Energy

II. Thermal Energy

(p.134-137, 141-144)

Temperature

Thermal Energy

Heat Transfer

a temperature
A. Temperature
  • Temperature
    • measure of the average KE of the particles in a sample of matter
b thermal energy
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
b thermal energy1

80ºC

80ºC

400 mL

A

B

200 mL

B. Thermal Energy
  • Which beaker of water has more thermal energy?
    • B - same temperature, more mass
c heat transfer
C. 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
c heat transfer1

80ºC

10ºC

A

B

C. Heat Transfer
  • 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.
c heat transfer2
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)
c heat transfer3

50 g Al

50 g Cu

C. Heat Transfer
  • Which sample will take longer to heat to 100°C?
  • Al - It has a higher specific heat.
  • Al will also take longer to cool down.
c heat transfer4

– Q = heat loss

+ Q = heat gain

T = Tf - Ti

C. Heat Transfer

Q = m T  Cp

Q: heat (J)

m: mass (kg)

T: change in temperature (K or °C)

Cp: specific heat (J/kg·K)

c heat transfer5

Coffee cup Calorimeter

C. Heat Transfer
  • Calorimeter
    • device used to measure changes in thermal energy
  • in an insulated system,

heat gained = heat lost

c heat transfer6
C. Heat Transfer
  • 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 = 0.032 kg

T = 20°C - 60°C = – 40°C

Q = (0.032kg)(-40°C)(235J/kg·K)

Q = – 301 J

c heat transfer7
C. Heat Transfer
  • 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