HEAT AND TEMPERATURE

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HEAT AND TEMPERATURE

• Chapter 4 in Tillery

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THE KINETIC MOLECULAR THEORY

• In the 5th century B.C. the Greek philosopher
  Democritus proposed that matter was composed of
  small indivisible particles called atoms. Only a
  vacuum existed between the atoms.
• Aristotle, 3rd century B.C., would not accept the
  concept of a vacuum and thus thought matter was
  continuous thus not composed of atoms.
• Galileo and Newton believed in the idea of matter
  being composed of small particles, because it
  seemed to be consistent with the nature and
  behavior of matter.
• During the late 1700s and into the early 1800s,
  strong evidence from chemical studies supported
  the idea of atoms and led to a series of
  inferences about atoms and their motion and
  behavior. These inferences are referred to as
  the Kinetic Molecular Theory.

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ATOMS AND MOLECULES IN MOTION

• The kinetic molecular theory is based on 3
  inferences 1) all matter is composed of small
  particles called atoms 2) the particles of
  matter are in constant motion 3) all collisions
  are perfectly elastic.
• The atom is the basic building block of pure
  substances called elements. An atom cannot be
  divided into smaller particles and still keep the
  characteristics of a particular element.
• There are also pure substances referred to as
  compounds. Some compounds are composed of tightly
  bound groups of atoms called molecules (example
  the water molecule).
• A molecule may be defined as the smallest
  particle of a compound or a gaseous element that
  can exist and still retain the characheristic
  properties of that substance. (Tillery, 2007).
• When a gas molecule collides with the wall of a
  container, it exerts a force called pressure on
  the container.

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MOLECULES INTERACT AND ARE ATTRACTED TO EACH OTHER

• Cohesion attractive forces of the same kind of
  molecules for each other.
• Adhesion attractive forces between unlike
  molecules.

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PHASES OF MATTER

• The physical state (phase) of a substance depends
  mostly on the chemical bonding in the substance
• Solids Solid particles are arranged in a
  definite pattern. Solids have both a definite
  shape and a definite volume
• Liquids Liquid particles appear to vibrate
  around moving points, but actually travel in
  straight-line paths between collisions. Liquids
  have a definite volume but assume the shape of
  their containers
• Gases Gas particles travel independently in
  straight-line paths. Gases assume the shape and
  volume of their container.
• Plasmas - A plasma is composed of electrons and
  positive ions at very high temperatures.

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http//abyss.uoregon.edu/js/21st_century_science/
lectures/lec05.html
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TEMPERATURE AND MOLECULAR MOTION

• Temperature is a measure of the average kinetic
  energy of the molecules making up a substance.
• KE ½ mv2
• See Figure 4.4, p. 88 in text.

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THERMOMETERS AND THERMOMETER SCALES

• Themomometers are really divices that measure the
  expansion or contraction of some material upon
  heating or cooling of the material
• The unit we use for meausrement of temperature is
  usually "degrees" (). Actually, there are three
  temperature scales that are used today. The
  Kelvin(K) scale is used by scientists. The
  Celsius scale (C) is used in most of the world
  to measure air temperatures and other
  temperatures, but is also sometimes used by
  scientists. In the United States, the Fahrenheit
  scale (F) is used to measure air temperatures,
  body temperatures, etc.
• The Fahrenheit Scale Developed by the German
  Physicist Fahrenheit in 1715. Originally a
  centigrade scale based on two reference points.
  An ice and salt water mixture for zero reference
  point and the temperature of the human body
  (taken to be 100) for the upper reference point.
  It was later found out that there is quite a
  range of human body temperature, with the average
  at 98.6 degrees Fahrenheit.
• The Celsius Scale Invented by a Swedish
  astronomer, Celsius, in 1735. This scale is also
  based on two arbitrary reference points and was a
  centrigrade scale. The lower reference point,
  representing zero degrees Celsius, was the
  freezing/melting point of pure water. The upper
  reference point, representing 100 degrees
  Celsius, was the boiling point of pure water at
  Standard Barometric Pressure.
• The Kelvin Scale Devised by William Thompson
  (Lord Kelvin) in 1848. This is not a relative
  scale with an arbitrary zero point, but has as
  its lowest point absolute zero the coldest
  possible temperature.

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http//go.hrw.com/resources/go_sc/hst/HP1PE730.PDF
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HEAT AND INTERNAL ENERGY

• Temperature and heat are not the same concepts.
• As we have already stated, temperature is a
  measure of the average kinetic energy of the
  molecules of a substance.
• The internal energy of a substance is the total
  kinetic and potential energy of the molecules of
  a substance.
• Heat is a measure of the internal energy that has
  been absorbed or transferred from one body (or
  substance) to another.
• Heat energy may be transferred from a body at
  higher temperature to a body at a lower
  temperature, or heat energy may be gained by a
  body during an energy form conversion. An energy
  form conversion actually does work on the
  molecules in a substance to speed them up.

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INTERNAL ENERGY
http//hyperphysics.phy-astr.gsu.edu/hbase/thermo/
inteng.html
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HEAT AS ENERGY TRANSFER
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MEASURES OF HEAT

• Heat is a form of energy. We have already stated
  that the Joule is the SI unit for energy.
  Therefore, the SI unit for heat energy is the
  Joule.
• However, scientists often use the calorie to
  measure heat. A calorie is the heat required to
  raise the temperature of 1 gram of water by 1
  degree Celsius. The nutritionists Calorie is
  really a kilocalorie, which is the heat required
  to raise the temperature of 1 kg of water by 1
  degree Celsius.
• One calorie is equivalent to 4.184 J.
• In the English system, the BTU (British Thermal
  Unit) is used to measure heat. A BTU is the heat
  required to increase the temperature of 1 pound
  of water by one degree Fahrenheit.

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SPECIFIC HEAT

• When heat is transferred, the amount of heat lost
  or gained by a substance is directly proportional
  to the change in temperature.
• Also when heat is transferred, the amount of heat
  lost or gained by a substance is directly
  proportional to the mass of the substance.
• And certainly different substances require
  different amounts of heat to go through the same
  temperature change. This is referred to as the
  specific heat of the substance.
• The specific heat of a substance may be defined
  as the amount of heat required to increase the
  temperature of one gram of the substance by one
  degree Celsius.
• See Table 4.2 in your text for specific heats of
  materials.

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PHASE TRANSITIONS NO TEMPERATURE CHANGE
Latent Heat Of Fusion (solid - liquid
transitions) Qf m Lf
Latent Heat Of Vaporization ((liquid - gas
transitions) Qv m Lv
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Heat flow

• Three mechanisms for heat transfer due to a
  temperature difference
• Conduction
• Convection
• Radiation
• Natural flow is always from higher temperature
  regions to cooler ones

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Conduction

• Heat flowing through matter
• Mechanism
• Hotter atoms collide with cooler ones,
  transferring some of their energy
• Direct physical contact required cannot occur in
  a vacuum
• Poor conductors insulators (Styrofoam, wool,
  air)

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Sample conductivities
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Convection

• Energy transfer through the bulk motion of hot
  material
• Examples
• Space heater
• Gas furnace (forced)
• Natural convection mechanism - hot air rises

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Radiation

• Radiant energy - energy associated with
  electromagnetic waves
• Can operate through a vacuum
• All objects emit and absorb radiation
• Temperature determines
• Emission rate
• Intensity of emitted light
• Type of radiation given off
• Temperature determined by balance between rates
  of emission and absorption
• Example Global warming

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Energy, heat, and molecular theory

• Two responses of matter to heat
• Temperature increase within a given phase
• Heat goes mostly into internal kinetic energy
• Specific heat
• Phase change at constant temperature
• Related to changes in internal potential energy
• Latent heat

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Evaporation and condensation

• Individual molecules can change phase any time
• Evaporation
• Energy required to overcome phase cohesion
• Higher energy molecules near the surface can then
  escape
• Condensation
• Gas molecules near the surface lose KE to liquid
  molecules and merge

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Thermodynamics

• The study of heat and its relationship to
  mechanical and other forms of energy
• Thermodynamic analysis includes
• System
• Surroundings (everything else)
• Internal energy (the total internal potential and
  kinetic energy of the object in question)

• Energy conversion
• Friction - converts mechanical energy into heat
• Heat engines - devices converting heat into
  mechanical energy
• Other applications heat pumps, refrigerators,
  organisms, hurricanes, stars, black holes, ,
  virtually any system with energy inputs and
  outputs

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The first law of thermodynamics

• Conservation of energy
• Components
• Internal energy
• Heat
• Work
• Stated in terms of changes in internal energy
• Application heat engines

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The second law of thermodynamics

• Equivalent statements
• No process can solely convert a quantity of heat
  to work (heat engines)
• Heat never flows spontaneously from a cold object
  to a hot object
• Natural processes tend toward a greater state of
  disorder (entropy)

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END