Introduction to Thermochemistry Chapter 16. 1, pp. 531-534

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Introduction to ThermochemistryChapter 16. 1,
pp. 531-534

• Temperature is a measure of the average kinetic
  energy of the particles in a sample of matter.
• Kinetic energy energy of movement
• The greater the kinetic energy, the higher the
  temperature.
• In chemistry, we use Celsius thermometers to
  measure temperature, but we convert them to a
  temperature scale called the Kelvin scale.
• K oC 273.15

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Example

• The Celsius temperature is 25 degrees. What is
  the Kelvin temperature?
• K oC 273.15
• K 25o 273.15
• K 298.15 or 298
• Notice 2 things 1) there is NO unit or degree
  marking for Kelvin temperatures 2) We can
  usually round the .15 down

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Measuring Energy Change

• All chemical and physical changes are accompanied
  by energy changes.
• We usually measure this in an object called a
  calorimeter. There are several different types
  of calorimeters, but they are all insulated and
  enclosed to capture all energy associated with
  energy changes.

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Heat

• Heatthe energy transferred between samples of
  matter because of a difference in their
  temperatures.
• Heat always is spontaneously transferred from the
  matter with the highest temperature to the matter
  with the lowest temperature.
• How much heat is transferred depends upon a lot
  of variables.

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Specific Heat

• Some variables involved in heat transfer include
  
• 1. Mass of the matter
• 2. Composition of the matter
• 3. Differences in the temperatures of the matter
  involved.
• Differences in the ability of matter to absorb
  heat is due to their composition. We use a
  property called specific heat to measure the
  difference.

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Specific Heat

• Specific heat of a substancethe amount of energy
  required to raise 1 gram of the substance 1
  Celsius degree or 1 Kelvin
• Every substance has a different specific heat, so
  we can use this property for identification
  purposes.
• Page 533 in your book has a chart of some
  specific heat values.

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Specific Heat

• Specific heat has units of J/g-K, which is Joules
  per gram-Kelvin or we can use J/g-oC (Joules per
  gram-Celsius degree)
• There are 2 equations we use with specific heat
  (Copy these from the board power point does not
  show them well)

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Specific Heat

• cp specific heat
• q energy lost or gained
• M mass of sample
• T change in temperature
• See pages 533-534 for examples of specific heat
  problems.