thermal energy transfer and absorption. thermodynamics thermodynamics-study of heat transformations...
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Thermal EnergyTransfer and absorption
Thermodynamics
Thermodynamics-study of heat transformations into other forms of energy
Heat
Fire dissipates heatDoes not absorb heat
Heat always flows from a hotter to cooler
Heat flowing from hotter to cooler
Grease fire
http://www.gocolumbiamo.com/Fire/Educational/stovefires.phphttp://www.teachertube.com/view_video.php?viewkey=d76c5ec1acefe6d433b6http://www.teachertube.com/view_video.php?viewkey=e0da400d9b98c254b9fc
Thermal Energy
Thermal Energy- total energy of the molecules
Temperature- related to average energy per molecule
Thermal Energy and Temperature
Temperature-quantifies the average kinetic energy of the particles in an objectThe warmer an object the more kinetic
energy it has.KEavg=KEt/(number of particles)
Thermal Energy- proportional to the number of particles
Equilibrium and Thermometry
Hot = particles move faster = more thermal energy
Conduction-transfer of kinetic energy when particles collideenergy transferred from a warmer object to a colder object
How much energy is in an object at 0 Kelvin (absolute zero)?
“Scientists put a light wave on hold”
http://www.msnbc.msn.com/id/3077366/
Equilibrium and Thermometry
Thermal Equilibrium- the state in which the rate of energy flow between two objects is equal and the objects are at the same temperatureSame temperature
Temperature Scales
Celsius- The zero point is the freezing point of
waterThe 100 point is the boiling point of
water
KelvinThe zero point is where all thermal
energy has been removed. No lower possible temperature, No motion in the atoms. Absolute Zero
0 K =- 273.15 CTc + 273 = TK
Temperature Scales
FahrenheitThe zero point is determined by a
frigorific mixture of ice, water, and ammonium chloride (a salt). The mixture automatically stabilizes its temperature at 0 °F
The second point is the 32 degree found by putting the thermometer in still water as ice is just forming on the surface.
The third point, the 96 degree, was the level of the liquid in the thermometer when held in the mouth or under the armpit. (Has been since adjusted to 98.6)
Three Temperature Scales
Three Temperature Scales
HeatAnd how it transferred
Heat
Heat-energy that always flows from the hotter object to the cooler object. “Left to itself heat never flows from a colder
object to a hotter object.”
Variable ‘Q’ denotes heatQ is in joules or J
Flow of Thermal Energy
Conduction
Convection
Radiation
Conduction
Heat is transferred (conducted) through particles that are in direct contact with each other.
Convection
The motion of fluid in a liquid or gas caused by temperature differences
Hotter fluids/gases rise.Cooler fluids/gases sink.
“Real power from nothing but hot air”http://www.guardian.co.uk/environment/2002/aug/19/energy.renewableenergy
Radiation
The transfer of energy by electromagnetic waves
Does not require contactTravels at 3x10^8 m/s
Nuclear Test Site, Ground Zero
Specific Heat
The amount of energy that must be added to a material to raise the temperature of a unit mass by one temperature unit.
Heat Transfer
Q = mC∆T = mC(Tf –Ti)
Q = heatm = massC = specific heatT = temperature
Temperature intervals for Kelvin and Celsius are the same, (i.e. ∆T is the same)
Ex 1, pg318 3-5 , pg 319
Conservation of Energy
The total energy in an isolated, closed system never changes.
EA + EB = constant
1)
2) 0
3)
A A A B B B
A A A B B Bf
A A B B
E q mC T
m C T m C T
m C T m C TT
m C m C
Ex 2, pg321 6-7, pg321
Homework
Pg 322 # 10, 12, 16, 17
Pg 336#37, 39, 50, 52, 53, 57
Changes of State and the Laws of Thermodynamics
Change in state changes structure and the way in which atoms store thermal energy
States of matter
SolidLiquidGasPlasma
Change-of-State
Changes of State
Melting Point Heat of FusionQ=mHf
Boiling PointHeat of VaporizationQ=mHv
Condensation PointFreezing Point
Heat = Q in Joules J
Thermal energy
Increase thermal energy Increases particle speedCauses more freedom of movement
Change-of-State
All thermal energy added goes to overcome the forces holding the particles together. The temperature does not increase
Melting
Boiling
The First Law of Thermal Dynamics
Change in thermal energy is equal to the heat added minus the work done
∆U=Q-WWhere
∆U is the change in thermal energyQ is the heat addedW is the work done
Efficiency
W/QH
How your refrigerator works
The Second Law of Thermal Dynamics
Natural processes go in a direction that maintains of increases the total entropy of the universe.
Things get more disordered over time, assuming time is going forward.
The Animate and the Inanimate(available on class website)
Read Pg 4-8,42 Explain what it means
One page write-up
Entropy
Entropy – the measure of disorder in a system
Change in Entropy – is equal to the heat added divided by the temperature in kelvins
∆S=Q/T
The measure of unavailability of useful energy
Temperature and Thermal Energy
Describe thermal energy and compare it to potential and kinetic energies.
Distinguish between temperature and thermal energy
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