CHAPTER 17.1: THE FLOW OF ENERGY

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CHAPTER 17.1THE FLOW OF ENERGY HEAT WORK
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OBJECTIVES

• I will be able to explain how energy, heat, and
  work are related
• I will be able to classify processes as
  endothermic/exothermic
• I will be able to distinguish between heat
  capacity and specific heat

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ENERGY TRANSFORMATIONS

• Thermochemistry study of energy changes that
  occur during chemical reactions and changes in
  state

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ENERGY TRANSFORMATIONS

• Energy the capacity for doing work or supplying
  heat

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ENERGY TRANSFORMATIONS

• Chemical potential energy energy stored in the
  chemical bonds of a substance
• Amount of stored energy depends on the kinds of
  atoms and their arrangements in a substance

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ENERGY TRANSFORMATIONS

• Work (w) energy required to move any object
  against some force

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ENERGY TRANSFORMATIONS

• Work and Energy
• Work is a form of energy
• The more energy a substance has, the more work
  that can be done

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ENERGY TRANSFORMATIONS

• Heat (q) energy that is transferred from one
  object to another because of their temperature
  differences
• Heat flows from warmer object to a cooler object
• When heat (energy) is transferred, temperatures
  rise

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ENERGY TRANSFORMATIONS

• Heat and Work
• Heat can be used to do work
• Work can be transferred into heat

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EXOTHERMIC ENDOTHERMIC PROCESSES

• System part of the universe in which you focus
  your attention
• Surroundings include everything else in the
  universe

• Major goal of thermochemistry is to examine the
  flow of heat between a system its surroundings

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EXOTHERMIC ENDOTHERMIC PROCESSES

• According to the law of conservation of energy,
  in any chemical or physical process, energy is
  neither created nor destroyed
• If energy of system decreases then the energy of
  the surroundings must increase by the same amount
  so that the total energy remains unchanged

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EXOTHERMIC ENDOTHERMIC PROCESSES

• In thermochemical calculations, the direction of
  heat flow is given from the point of view of the
  system

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EXOTHERMIC ENDOTHERMIC PROCESSES

• Endothermic process a process in which the
  system absorbs heat from its surroundings
• System gains heat, surroundings cool down
• Heat flowing into a system from surrounding is
  defined as positive ()
• q has a positive value
• Breaking a chemical
• bond requires energy

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EXOTHERMIC ENDOTHERMIC PROCESSES

• Exothermic process a process in which the
  system releases heat to its surroundings
• System loses heat, surroundings heat up
• Heat flowing out of system to its surrounding is
  defined as negative (-)
• q has a negative value
• Heat is lost
• Forming a chemical bond
• releases energy

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UNITS FOR MEAUSRING HEAT FLOW
1 J 0.2390 cal 4.184 J 1 cal

• Heat flow is measured in
• The joule (J)
• 1 J of heat raises the temperature of pure water
  0.2390 C
• The calorie (cal)
• The quantity of heat needed to raise the
  temperature of 1 g of pure water 1 C
• When dealing with food we use Calorie not calorie
• Energy in food

1 Calorie 1 kilocalorie 1000calories
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HEAT CAPACITY AND SPECIFIC HEAT

• Heat capacity is the amount of heat needed to
  increase the temperature of an object exactly 1
  ?C
• Dependent upon objects mass and chemical
  composition
• Greater the mass, the greater the heat capacity

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HEAT CAPACITY AND SPECIFIC HEAT

• Specific heat (C) of a substance is the amount of
  heat it takes to raise the tempearute of 1 g of a
  substance
• Water has a very high specific heat

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SAMPLE PROBLEM 17.1

• The temperature of a 95.4-g piece of copper
  increases from 25.0 ?C to 48.0 ?C when the copper
  absorbs 849 J of heat. What is the specific heat
  of copper?