ch. 5 - energy ii. thermal energy (p.134-137, 141-144) temperature thermal energy heat transfer
TRANSCRIPT
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Ch. 5 - EnergyCh. 5 - Energy
II. Thermal Energy(p.134-137, 141-144) Temperature Thermal Energy Heat Transfer
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A. TemperatureA. Temperature
Temperature measure of the
average KE of the particles in a sample of matter
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Measuring TemperatureMeasuring Temperature
A thermometer is a instrument for measuring temperature.
Uses a standard for comparison.Examples: Celsius, Fahrenheit, and
Kelvin Scales
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Celsius Scale (Celsius Scale (ooC)C)
Based on freezing point (0oC) and boiling point (100oC) of water
Standard metric scale for measuring particle temperature
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Kelvin Scale (K)Kelvin Scale (K)
Using absolute zero as a standardAbsolute zero is the temp. where
kinetic molecular motion stopsConversion: (273.15+ oC)= Kelvin
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Temperature vs. HeatTemperature 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
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Temp. vs. HeatTemp. vs. Heat
Heat: Energy given off or absorbed by
an object Measures the motion of molecules
in an object Measured in Calories
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B. Thermal EnergyB. 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
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B. Thermal EnergyB. Thermal Energy
Which beaker of water has more thermal energy? B - same temperature, more mass
200 mL
80ºC
A400 mL
80ºC
B
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Thermal Energy Cont.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.
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C. Heat TransferC. 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
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C. Heat TransferC. Heat TransferWhy does A feel hot and B feel cold?
80ºC
A
10ºC
B
Heat flows from A to your hand = hot. Heat flows from your hand to B = cold.
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C. Heat TransferC. 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)
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Specific Heat Cont.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
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C. Heat TransferC. 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.
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C. Heat TransferC. 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)
T = Tf - Ti
– Q = heat loss+ Q = heat gain
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C. Heat TransferC. Heat Transfer
Calorimeter device used to
measure changes in thermal energy
Coffee cup Calorimeter
in an insulated system,
heat gained = heat lost
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C. Heat TransferC. Heat TransferA 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
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C. Heat TransferC. Heat TransferHow 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
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Forms of Heat TransferForms of Heat Transfer
Three forms of Heat Transfer:
(6.1- pgs 152- 158) Conduction
Convection
Radiation
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ConductionConduction
Conduction involves the transfer of heat through direct contact
Heat conductors conduct heat well, insulators do not
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ConvectionConvection
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
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Fluid ConvectionFluid Convection
Currents are formed be the movement of liquids and gases from warmer to cooler areas.
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RadiationRadiation
Heat transferred through space
Energy from the sun being transferred to the Earth
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Thermal Pollution (5.3- 138-140)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