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Chapter 16 Energy and Chemical Change

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... of heat changes that accompany chemical reactions and ... Chapter 16 Energy and Chemical Change Nature of energy Measuring heat Calories ... – PowerPoint PPT presentation

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Title: Chapter 16 Energy and Chemical Change


1
Chapter 16 Energy and Chemical Change
2
Nature of energy
  • Energy the ability to do work or produce heat
  • Kinetic energy energy of motion
  • Potential energy stored energy
  • Chemical potential energy stored energy because
    of composition

3
Measuring heat
  • Heat energy process of flowing from a warmer
    object to a cooler object
  • Calorie the amount of heat required to raise
    the temperature one degree Celsius
  • Joule SI unit of heat and energy

4
Calories
  • When your body breaks down sugars and fats to
    form carbon dioxide and water, these exothermic
    reactions generate heat that can be measured in
    Calories

5
Specific Heat
  • Specific heat amount of heat required to raise
    the temperature of one gram of that substance by
    one degree Celsius
  • Units - J/g C
  • Large specific heats Large amount of energy to
    change temperature (water)
  • Small specific heats Small amounts of energy to
    change temperature (gold)

6
Calculating Heat
  • q m x c x ?T
  • q mc?T
  • q (heat)
  • c (specific heat)
  • m (mass of sample)
  • ?T (change in temperature)

7
Calculations
  • The temperature of a sample of iron with a mass
    of 10.0g changed from 50.4C to 25.0 C with the
    release of 114J heat. What is the specific heat
    of iron?
  • q mc?T
  • Heat (q)
  • 114J
  • Mass (m)
  • 10.0g
  • Specific Heat (c)
  • X
  • Change in temperature (?T)
  • 50.4C - 25.0 C 25.4 C
  • 114 10.0(x)25.4
  • 114 254(x)
  • X.44881
  • Final answer 0.449J/g C (3 significant figures
    and units)

8
Measuring Heat
  • Calorimeter insulated device used for measuring
    the amount of heat absorbed or released during a
    chemical or physical process

9
Thermochemistry
  • Thermochemistry is the study of heat changes that
    accompany chemical reactions and phase changes

10
Enthalpy
  • Enthalpy (H) is the heat content of a system at
    constant pressure
  • Enthalpy of reaction
  • ?HrxnHproducts Hreactants

11
Reactions
  • Endothermic absorbs heat giving the ?Hrxn a
    positive number
  • Exothermic releases heat giving the ?Hrxn a
    negative number
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