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Chapter 21 Temperature_ Heat_ and Expansion

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Chapter 21 Temperature_ Heat_ and Expansion Powered By Docstoc
					Temperature, Heat, and
     Expansion
        Chapter 21
               Temperature
 Temperature – the quantity that tells how hot
  or cold something is compared with a standard
 A common thermometer measures temperature
  by showing the expansion and contraction of a
  liquid in a glass tube using a scale
 Celsius Scale – most widely used temperature
  scale, 0ºC is the point at which water freezes
  and 100ºC the point at which water boils, the
  gap between is divided into 100 equal parts
            Temperature
 Fahrenheit Scale – commonly used in
  the U.S., has 180ºF between freezing and
  boiling (32ºF and 212º)
 Kelvin Scale – used in scientific
  research, degrees are the same size as
  Celsius + 273º, denoted K
 Absolute Zero – the lowest possible
  temperature on the Kelvin scale,
  substance has no kinetic energy
Thermometers
Scale Comparison
Temperature and Kinetic Energy
 In an ideal gas, temperature is
  proportional to the average kinetic energy
 The heat that you feel when you touch a
  hot surface is the kinetic energy
  transferred by molecules in the surface to
  molecules in your fingers
 Temperature is not a measure of the total
  kinetic energy
                       Heat
   Heat – the energy that transfers from one
    object to another because of a temperature
    difference between them
   Matter does not contain heat, but contains
    energy in several forms
   Heat is energy in transit
   Internal Energy – the energy resulting from heat
    flow
   When heat flows from one object or substance
    to another it is in contact with, the objects are
    said to be in thermal contact
   Heat flows from the higher-temperature
    substance into the lower-temperature substance
Heat Flow Between Two Gases
        Thermal Equilibrium
 Thermal Equilibrium – objects in
  thermal contact with each other reach the
  same temperature, no heat flows between
  them
 When reading a thermometer, we wait
  until the thermometer has reached
  thermal equilibrium with the object we
  want the temperature of
Thermal Equilibrium
           Internal Energy
 Internal Energy – the total of all
  energies inside a substance
 A substance does not contain heat – it
  contains internal energy
 When a substance takes in or gives off
  heat, any of these energies can change
Internal Energy
            Measurement of Heat
   To quantify heat, we have to specify the mass and
    kind of substance affected
   Calorie – the most commonly used unit for heat;
    the amount of heat required to raise the
    temperature of 1 gram of water by 1ºC
   Kilocalorie – the heat required to raise 1 kilogram
    of water by 1ºC (1000 calories)
   The heat unit for rating foods is actually the
    kilocalorie (to distinguish from calorie, it is often
    written as Calorie)
   Remember that a calorie is a measure of ENERGY!
   The relationship between calories and joules is:
                   1 calorie = 4.184 Joules
Calories
          Specific Heat Capacity
 Different substances have different capacities for
  storing internal energy
 We find that specific materials require specific
  quantities of heat to raise the temperature of a
  given mass of the material by a specified number of
  degrees
 Specific Heat Capacity – the quantity of heat
  required to raise the temperature of a unit mass of a
  substance by 1ºC
                        Q = mcΔT
    Q = quantity of heat; m = mass of substance;
        c = specific heat capacity of substance;
              ΔT = change in temperature
 We can think of specific heat capacity as thermal
  inertia (an object’s resistance to change)
Specific Heat Capacities
          Thermal Expansion
 When the temperature of a substance increases,
  the molecules “jiggle” faster and move further
  apart, causing an expansion of the substance
 Gases generally expand and contract more than
  liquids, which expand and contract more than
  solids
 In concrete sidewalks and highways this
  expansion and contraction is taken into account
  when it is being built. The surface is laid down
  in small sections with a gap in between, that is
  usually filled with a substance such as tar.
Thermal Expansion




    Expansion Joint
         Expansion of Water
 Almost all liquids will expand when they
  are heated, ice-cold water instead
  contracts to go from ice to a liquid
 When the water reaches a temperature of
  4ºC, it will stop contracting and begin
  expanding
 This has to do with the crystal structure of
  water, its solid state has an open structure
  that takes up more volume and is
  therefore less dense
Expansion of Water
Assignment – Due Tuesday 1/22
 Read Chapter 21 (pg. 307-321)
 Do Chapter 21 #19-39 (pg. 323-324)

				
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posted:1/17/2013
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