Temperature and Heat

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• Temperature and Heat
• Temperature a measure of the average kinetic
  energy of all the particles within an object
  (movement of atoms)
• Faster the movement, the higher the temperature
• Heat the transfer of thermal energy from the
  particles of one object to those of another
  object due to a temperature difference between
  the two objects
• Heat always flows from an object with higher
  temperature to an object with lower temperature
• Heat is thermal energy in transit
• Thermal energy total energy in an object
  including but not limited to the kinetic,
  potential, chemical, electrostatic, etc
• 2 liters of boiling water vs. 1 liter of boiling
  water
• Which has the higher temperature (more average
  kinetic energy)? Which has more thermal energy?
• Objects do not have heat, they have energy.

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• Temperature Scales
• freezing boiling room temp
• Fahrenheit 32 212 70
  
• Celsius 0 100 21
• Kelvin 273 373 294
• Formulas
• Fahrenheit to Celsius TC TF 32
• 
  1.8
• Celsius to Fahrenheit TF1.8TC 32
• Celsius to Kelvin TK TC 273
• Kelvin to Celsius TC TK 273

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• Practice Problems-temperature scales
• Air in the living room (21 C )
• Metal in a running car engine ( 388 K)
• Liquid nitrogen (-200 C)
• Air on a summer day in the desert (110 F)
• Normal body temperature (98.6 F)

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What is absolute zero? Temperature when
particles have no kinetic energy 0 K or -273
C Do molecules of lemonade or hot soup have more
KE? Hot soup b/c it is at a higher
temperature What precautions should you take at
100 K vs. 100 C? 100 K is very cold (warm
clothes) 100 C is very hot (need fire
protection) Of Lake Michigan and a cup of
boiling water Which has a higher temperature?
More total kinetic energy?
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Energy Transfer Conduction Convection Radiation
Conduction transfer of
energy as heat between particles as they collide
within a substance. This happens when the two
objects are in contact at unequal temperatures.
Resultheat transfer Rapidly moving particles of
one substance transfer some energy to slowly
moving particles nearby through contact (rapidly
moving atoms collide with slower atoms and
transfer energy) Examples roasting
marshmallows with metal skewer over a fire pot
on the stove in contact with the element
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Heat transfer continued Convection transfer of
energy by fluids of different temperatures fluids
are either gasses or liquids The heated fluid
rises, cools as it gains distance, and falls. As
it is heated, the fluid becomes less dense so it
rises. It then cools, becomes more dense, and
sinks (creating a convection current created by
expansion and contraction). Examples heating
and cooling a building campfire when it warms
the air Movement of heated substance itself
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Energy transfer continued Radiation transfer
of energy by electromagnetic waves
(infrared, visible light, ultraviolet) Does not
involve movement of matter like conduction and
convection Energy is being radiated through
empty space Examples heat from the sun and
from a fire (off to the side) Which would absorb
more heat energy a light or dark can? Why?
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Conductors and insulators Conductor is a
material through which energy can be easily
transferred as heat Examples? Insulator is a
material that is a poor conductor of energy
(slows the transfer of energy as heat) Note
a blanket doesnt give off heat, it traps a
persons body heat Examples? Not all substances
absorb energy as heat in the same way
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• Specific heat
• Defined as the amount of energy that must be
  transferred to a substance to raise the
  temperature of 1 kg of that substance by 1K.
• May also be defined using 1 g and 1C
• Units are measured in Joules/kg K
• Heat energy Q (unit Joule or J)
• Specific heat c (unit J/kg K or J/g K or J/kg
  C or J/g C)
• Mass m (unit kg or g)
• ?T temperature change Tfinal T initial
• Qmc?T
• Other units of energy calorie and Calorie
• 1Calorie 1000 calories
• 1calorie 4.184 Joules
• BTU (amount of energy required to raise 1 lb of
  water by 1F)

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• Steam 1.870
• Ammonia (gas) 2.060
• Ethanol (liquid) 2.440
• Aluminum 0.897
• Carbon (graphite) 0.709
• Copper 0.385
• Gold 0.129
• Iron 0.449
• Mercury 0.140
• Lead 0.129
• Silver 0.234

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• Practice Problems with specific heat
• How much energy must be transferred as heat to
  the 420 kg of water in a bathtub in order to
  raise the waters temperature from 25C to 37C?

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• What mass of water is required to absorb 4.7 x
  105 J of energy from a car engine while the
  temperature increases from 298 K to 355K?

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• A vanadium bolt gives up 1124 J of energy as its
  temperature drops 25K. If the bolts mass is
  93g, what is its specific heat?

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• How much energy is needed to increase the
  temperature of 755g of iron from 283 K to 403 K?

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• How much energy must a refrigerator absorb from
  225 g of water so that the temperature of the
  water will drop from 35 to 5C