Temperature and Kinetic Theory

1
Temperature and Kinetic Theory
2
Atomic Theory

• Atom smallest piece of mater
• Atomic Mass
• ? unit atomic mass unit amu
• ? 1amu 1.66 x 10-27 kg
• Molecular Mass - sum of all masses in molecules
• Brownian motion atoms are in continuous motion

3
Examples

• What is the atomic mass of He in amu? What is
  this mass in kg?
• What is the molecular mass of Fe2O3 in amu? What
  is this mass in kg?

4
Properties

• Atoms and molecules exert attractive and
  repulsive forces on each other
• Solids attractive forces are strong enough to
  hold the particles in fixed positions
• Liquids move faster, forces are weaker,
  particles roll over one another
• Gases forces very weak, particles do not stay
  together

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Temperature

• Measure of average kinetic energy (speed)
  higher temperature means particles are on average
  moving faster
• Many properties change with temperature size,
  electrical resistance, color of light emitted
• Thermometer instrument that measures
  temperature (relies on expansion of materials)

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Temperature Scale

• Celsius
• C 5/9 (F 32)
• F 9/5C 32
• Kelvin scientific scale
• K C 273.15
• O K absolute zero all atomic motion stops

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Thermal Equilbrium

• When two objects of different temperature are
  placed in contact, they will eventually reach the
  same temperature
• Heat flows from high temp. to low temp.
• Zeroth Law of Thermodynamics if two systems are
  in thermal equilibrium with a third system, then
  they are in thermal equilibrium with each other

8
Thermal Expansion

• Expansion of a material due to an increase in
  temperature
• Amount a substance expands or contracts depends
  on the material
• The amount the length changes is directly
  proportional to the amount the temp changes and
  the original length

9
Expansion Equations - Solids

• ?L ?Lo?T
• ? - coefficient of linear expansion which
  depends on the material (pg.344)
• A 2?Ao?T
• V 3?Vo?T

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Example

• A steel bed of a suspension bridge is 200m long
  at 20C. If the extreme temperatures are -30C
  and 40C, how much will it contract or expand?

11
Example

• An iron ring is to fit snug on a cylindrical iron
  rod. At 20C, the diameter of the rod is 6.445cm
  and diameter of the ring is 6.420cm. To slip
  over, the ring must be slightly larger than the
  rod by about .008cm. To what temperature must the
  ring be heated?

12
Volume Expansion - Liquid

• Volume change of the liquid can be related by a
  similar equation
• ?V ?Vo?T
• ?-coefficient of volume expansion

13
Example

• A 70L steel gas tank is filled at 20C. The car
  is left to sit in the sun and the tank reaches
  40C. How much gas would overflow from the tank
  (if any)?