Thermochemistry -- The Flow of Energy: Heat --

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Thermochemistry-- The Flow of Energy Heat --

• Thermochemistry the study of heat changes in
  chemical reactions
• Chemical potential energy energy stored within
  the structural units of chemical substances

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Thermochemistry-- The Flow of Energy Heat --
Chemical System Types Chemical System Types Chemical System Types
System type Description ?q (change in heat)
Endothermic System absorbing heat from the surroundings ?q gt 0
Exothermic System releasing heat to the surroundings ?q lt 0
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Thermochemistry-- The Flow of Energy Heat --

• Law of Conservation of Energy
• In any chemical or physical process, energy is
  neither created nor destroyed

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Thermochemistry-- The Flow of Energy Heat --

• The calorie
• Expressed as a c (lower case)
• Quantity of heat needed to raise the temperature
  of 1 g of pure water 1?C
• Calorie
• Expressed as a C (upper case)
• Dietary Calorie
• 1 Calorie 1 kilocalorie 1000 calories

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Thermochemistry-- An Intro Video --
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Thermochemistry-- The Flow of Energy Heat --

• Joule
• SI unit of heat and energy
• Raises the temperature of 1 g of pure water
  0.2390?C
• 4.184 J 1 cal
• Heat Capacity
• Amount of heat needed to increase the temperature
  of an object exactly 1?C
• Will change depending on the mass and chemical
  composition
• Specific Heat
• Quantity of heat needed to raise the temperature
  of
• 1g of substance 1oC

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Thermochemistry-- The Flow of Energy Heat --

• Specific Heat Capacity
• Heat (q) specific heat capacity (C)
• Mass (m) change in temperature (?T)
• q mC ?T

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Thermochemistry-- The Flow of Energy Heat --

• Example
• How many kilojoules of heat are absorbed when
  1.00 L of water is heated from 18?C to 85?C?
• Solution
• q mC?T
• q 1000g x 4.18 J x 67oC
• g o C
• q 2.8E5 J 1 KJ
• 1000 J
• 280 KJ

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Thermochemistry-- The Flow of Energy Heat --

• Example
• A chunk of silver has a heat capacity of 42.8
  J/?C. If the silver has a mass of 181 g,
  calculate the specific heat of silver.
• Solution
• q mC?T
• 42.8 J 181g x C x 1OC
• C 0.236 J/goC

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Thermochemistry-- Measuring and Expressing Heat
Changes --

• Your Turn
• The temperature of a piece of copper with a mass
  of 95.4 g increases from 20.0oC to 40.0oC when
  the metal absorbs 849 J of heat. What is the
  specific heat of copper?
• q mC?T
• 849 J 95.4g x C x 23.0oC
• C 0.387 J/g x oC

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Thermochemistry-- Measuring and Expressing Heat
Changes --

• Calorimeter