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Thermal Energy & Thermal Energy & HeatHeat
What is Temperature?What is Temperature?
Temperature measure of the average KE of all the particles within an object
Temperature ConversionsTemperature Conversions
oC to oF: oF = 9/5(oC) + 32oF to oC: oC = 5/9(oF – 32)oC to K: K = oC + 273K to oC: oC = K – 273
Going from Celsius to Going from Celsius to FahrenheitFahrenheit
Convert 37 oC to oF.oF = 9/5(oC) + 32oF = 9/5(37oC) + 32
= 66.6 + 32
= 98.6oF
Going from Fahrenheit to Going from Fahrenheit to CelsiusCelsius
Convert 68oF to oCoC = 5/9(oF – 32)oC = 5/9(68 – 32)
= 5/9(36)
= 20 oC
Going from Celsius to KelvinGoing from Celsius to Kelvin
Convert 100oC to K
K = oC + 273
K = 100 + 273
= 373 K
Going from Kelvin to CelsiusGoing from Kelvin to Celsius
Convert 310 K to oCoC = K – 273oC = 310 – 273
= 37oC
Thermal EnergyThermal 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
Thermal EnergyThermal Energy
Which beaker of water has more thermal energy? B - same temperature, more mass
200 mL
80ºC
A400 mL
80ºC
B
Heat TransferHeat 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
Heat TransferHeat 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.
Heat TransferHeat Transfer Heat is always
transferred from hot to cold.
Insulators slow the transfer of heat due to air pockets.
Conductors easily allow the transfer of heat, like metals.
Heat is transferred by conduction, convection, and radiation.
ConductionConduction
Heat is transferred due to objects touching each other or through collisions.
Occurs best in solids. Heat continues to be
transferred until both objects reach the same temperature, called a thermal equilibrium.
ConvectionConvection
Transfer of heat through a liquid or gas through moving currents, called convection currents.
The cause of wind and weather.
RadiationRadiation Transfer of heat
through electromagnetic radiation (light from stars or light bulbs).
Transferred in all directions.
No contact required! Dark or dull objects
absorb more than light or shiny objects do.
Heat TransferHeat 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/(g·°C)
Heat TransferHeat 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.
Heat TransferHeat Transfer
Q = m T Cp
Q: heat (J)m: mass (g)T: change in temperature (K or °C)Cp: specific heat (J/g·K or J/g.oC)
T = Tf - Ti
– Q = heat loss+ Q = heat gain
Heat TransferHeat Transfer
Calorimeter device used to
measure changes in thermal energy
Coffee cup Calorimeter
in an insulated system,
heat gained = heat lost
Heat TransferHeat 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
T = 293 K – 333 K = -40 K
Q = (0.032kg)(-40 K)(235J/kg·K)Q = -300.8 J (lost heat, negative)
Heat TransferHeat 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= 4.184 J/g·oC
WORK:
Q = m·T·Cp
m = 230 g
T = 90°C - 12°C = 78°C
Q = (230 g)(78oC)(4.184 J/g·oC)Q = 75,061 J (gained heat, positive)
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