15 Temperature, Heat, Expansion

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15 Temperature, Heat, Expansion

• Temperature Heat
• Internal Energy Specific Heat
• Homework
• RQ 1, 2, 7, 8, 10, 12, 15, 21, 24.

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Temperature

• T
• Ex hammered metal
• Expansion with T increase

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Superheating

• Mythbusters
• Instant coffee

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Water Expansion

• Water expands from 4C to 100C (as does most
  materials)
• However, water contracts when warmed from 0C to
  4C. (transient ice melting)

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Heat

• heat is a transfer of thermal energy due to
  temperature difference
• Examples
• ice in warm liquid heat flows from liquid to the
  ice
• warm liquid is put in a refrigerator heat flows
  from drink to the cold air in refrigerator
• //

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Internal Energy

• the total of all molecular energies, kinetic plus
  potential, that are internal to a substance. It
  is (mass) x (temperature).
• Heat ? Internal Energy,
• however, for a thermal-only process,
• Heat D(Internal Energy)

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mixing hot and cold warm

• for liquids solids heat (mass)x(temperature
  change)
• when hot and cold are mixed, heat lost by
  hot heat gained by cold
• Ex. 1kg water at 0C is mixed with 1kg water at
  20C
• (1kg)(T - 0) (1kg)(20 T)

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Calories and Joules

• 1 Calorie _______ calories
• 1 calorie ________ joule
• Calorie is the common food unit.
• Btus are also used, e.g. gas range

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Specific Heat

• quantity of heat required to raise the
  temperature of 1kg by 1C. //

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specific heat

• c Q/(mDT) J/(kgK)
• c heat/(massx temperature change)
• Water 4186 J/kgC
• heat needed per kg to raise temperature by 1
  degree C or K.

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summary

• T KE/molecule
• most substances undergo thermal expansion (note
  the water exception)
• heat is an exchange of thermal energy
• superheating
• specific heat heat needed to raise temp. of 1kg
  by 1C (substance dependent)