Unit 9: THERMODYNAMICS

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Unit 9THERMODYNAMICS
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Temperature Heat

• Thermodynamics
• Thermo Study of heat
• dynamics Movement of that heat between
  objects
• Thermometers
• Measure temperature based on physical properties
• Mercury based thermometers expand at a
  predictable rate with temperature
• Scale of the thermometer measures the amount of
  expansion

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Temperature scales

• Temperature scales
• Kelvin (K), Celsius (C), and Fahrenheit (F)
• Temperature values are different on each scale
• Comfortable indoor room temperature
• 68 F 20 C 293.15 K
• Water freezes at 0C 32F 273.15 K
• There are 100 degrees between the freezing
  boiling points of water on the Celsius scale, and
  100 Kelvins between the freezing and boiling on
  the Kelvin scale
• Units of these two scales are equal
• Unit of Celsius Unit of Kelvin

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Kelvin temperature
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Temperature Scale conversions

• TK TC 273.15
• TC (5/9)(TF 32)
• TK Kelvin Temperature
• TC Celsius Temperature
• TF Fahrenheit Temperature

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Converting from a Celsius to a Fahrenheit
Temperature A time and temperature sign on a
bank indicates that the outdoor temperature is
-20.0oC. Find the corresponding temperature
on the Fahrenheit scale.
Degrees below ice point
ice point
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Absolute Zero

• The lowest temperature any material could
  theoretically reach ? As cold as it can get!
• Reference point at which molecules are in their
  minimum energy state
• 0 K (-273.15 C -459.67 F)

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HEAT

• Thermal energy that flows from one object to
  another due to a temperature difference
• Energy flows from a higher-temperature object to
  a lower-temperature object because of the
  difference in temperatures.
• Example In an oven, heat flows from the oven
  coils to the air molecules, warming them up, and
  then to the bread, warming it as well
• Not a property of an object
• Represented by the letter Q
• SI Unit Joules (J)

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Internal Energy Energy associated with the
molecules and atoms that make up a system Heat
flows from hot to cold- originating from the
internal energy of the hot substance. It is not
correct to say that a substance contains heat.
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Endo/exothermic processes

• Endothermic Processes
• Absorb heat from the surrounding area(s)
• Cooling effect on the environment
• Exothermic Processes
• Release heat into the surrounding area(s)
• System becomes cooler ? Environment becomes warmer

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Oranges

• Farmers farm oranges in the winter (Oranges
  could freeze!)
• Farmers Prevention
• - Pour water on the oranges ? letting the water
  freeze instead!
• - Freezing gives off a lot of heat. So, when
  the water freezes, it gives the heat to the
  oranges
• - Freezing ? Exothermic ? The orange absorbs
  the heat from the water as the freezing occurs

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Cars cooling system

• http//auto.howstuffworks.com/cooling-system.htm

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SURROUNDINGS
HEAT
HEAT
HEAT
HEAT
SYSTEM
SYSTEM
EXOTHERMIC
ENDOTHERMIC
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EXOTHERMIC
ENDOTHERMIC
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Zeroth Law of Thermodynamics

• If objects A and B are in thermal equilibrium,
  and objects B and C are in thermal equilibrium,
  then A and C will be in equilibrium as well

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Thermal Expansion

• Thermal Expansion
• Increase in the length or volume of a material
  due to a change in its temperature
• Different materials expand at different rates

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Thermal Linear expansion

• Thermal Linear Expansion of a Solid
• Length an object changes when its temperature
  changes
• Measured along one dimension
• Coefficient of linear expansion, is a constant,
  that specifies how much a given material expands
  with a change in temperature
• Represented by greek letter alpha (a)
• Linear Expansion Equation
• ?L Li a ?T
• L Length
• a Coefficient of linear expansion
• ?T Change in temperature (K or C)

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THE BIMETALLIC STRIP
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NORMAL SOLIDS
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The Buckling of a Sidewalk A concrete sidewalk
is constructed between two buildings on a day
when the temperature is 25oC. As the temperature
rises to 38oC, the slabs expand, but no space is
provided for thermal expansion. Determine the
distance y in part (b) of the drawing.
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Thermal expansion of water

• Thermal expansion of water
• Above 4C, water contracts and sinks as it cools
• You may have experienced this effect if you have
  jumped into a lake
• The water is colder the deeper you go
• This chilling and sinking of the top layer
  continues until the lake is 4 C throughout
• From 4C to 0C, water expands and stays on top
• At 0C, water turns into ice and floats (less
  dense)
• Crucial for the survival of aquatic life

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Expansion of Water
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Thermal Volume expansion

• Volume of an object changes when its temperature
  changes
• Every substance has a coefficient of volume
  expansion (ß) ? varies by material
• ?V Vi ß?T
• V Volume
• ? Coefficient of volume expansion ?
• ?T Change in temperature
• ? 3a

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An Automobile Radiator A small plastic
container, called the coolant reservoir, catches
the radiator fluid that overflows when an
automobile engine becomes hot. The radiator is
made of copper and the coolant has an expansion
coefficient of 4.0x10-4 (Co)-1. If the radiator
is filled to its 15-quart capacity when the
engine is cold (6oC), how much overflow will
spill into the reservoir when the coolant
reaches its operating temperature (92oC)?
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Specific Heat Capacity

• Property of a material
• A constant that tells how much the temperature of
  a mass of material changes when a particular
  amount of heat is transferred
• A material with a large specific heat requires
  more heat per kilogram to a produce a given
  change in temperature than one with a smaller
  specific heat

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Specific heat capacity Equation

• Q cm?T
• Q Heat (J or calories)
• Q Negative, heat energy is removed
• Q Positive, heat energy is added
• c Specific heat (J/kg x K) or (cal/gC)
• m mass
• ?T Temperature change in C or K
• (?T Tf Ti)

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A Jogger In a half-hour, a 65-kg jogger can
generate 8.0x105 J of heat. This heat is removed
from the body by a variety of means, including
the bodys own temperature-regulating mechanisms.
If the heat were not removed, how much would the
body temperature increase?
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CALORIMETRY
If there is no heat loss to the surroundings, the
heat lost by the hotter object equals the heat
gained by the cooler ones.
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Measuring Specific Heat Capacity The calorimeter
is made of 0.15 kg of aluminum and contains 0.20
kg of water. Initially, the water and cup have
the same temperature of 18.0oC. A 0.040 kg mass
of unknown material is heated to a temperature
of 97.0oC and then added to the water. After
thermal equilibrium is reached, the temperature
of the water, the cup, and the material is
22.0oC. Ignoring the small amount of heat gained
by the thermometer, find the specific heat
capacity of the unknown material.
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Molar Specific Heat

• A constant that tells how much the temperature of
  a particular number of moles of a material
  changes when a particular amount of heat is
  transferred
• A mole of a substance is a measure of quantity
  based on the number of particles making up an
  object
• 1 mole 6.022 x 1023 molecules or atoms
• Q kn?T
• Q Heat (J)
• k Molar specific heat (J/mol x K)
• n Number of moles
• ?T Temperature change in C or K

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Phase changes

• Transformation between solid and liquid, liquid
  and gas, or solid and gas
• All require the addition of energy
• When water freezes into ice or steam condenses
  into water ? Energy is released
• Although energy is being added or released
  during a phase change ? Temperature of the
  substance remains constant

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THE PHASES OF MATTER
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During a phase change, the temperature of the
mixture does not change (provided the system is
in thermal equilibrium).
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Latent heat

• Energy required per kilogram to cause a phase
  change in a given material
• Latent heat of fusion
• Transforming from solid to liquid, or liquid to
  solid
• Latent heat of vaporization
• Transforming from liquid to gas, or vice-versa
• Latent heat values ? Same in either direction
  of phase change

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Latent heat

• Latent Heat Equations
• Q Lfm
• Q Lvm
• Q Heat (J)
• m Mass (kg)
• Lf Latent heat of fusion (J/kg)
• Lv Latent heat of vaporization (J/kg)

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Ice-cold Lemonade Ice at 0oC is placed in a
Styrofoam cup containing 0.32 kg of lemonade at
27oC. The specific heat capacity of lemonade is
virtually the same as that of water. After the
ice and lemonade reach an equilibrium
temperature, some ice still remains. Assume that
mass of the cup is so small that it absorbs a
negligible amount of heat.
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conduction

• Flow of thermal energy directly through a
  material without motion of the material itself
• Example Cast iron pan on stove ? Handle
  eventually gets hot
• Thermal Conductors
• Materials that conduct heat well
• Thermal Insulators
• Materials that conduct heat poorly

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convection

• Process in which heat is carried from one place
  to another by the bulk movement of a fluid
• Heat transfer through a gas or liquid caused by
  movement of the fluid

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Hot Water Baseboard Heating and
Refrigerators Hot water baseboard heating units
are mounted on the wall next to the floor. The
cooling coil in a refrigerator is mounted near
the top of the refrigerator. Each location is
designed to maximize the production of convection
currents.
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Radiation

• Radiation
• Heat transfer by electromagnetic waves
• Material that is a good absorber is also a good
  emitter

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Global warming

• Global Warming the Greenhouse Effect