1st Law of Thermodynamics

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1st Law of Thermodynamics

• U Q - W
• The change in internal energy of an object
  is equal to the heat added to the object minus
  the work done by the object.

See textbook p. 411 for table of Special Processes
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Internal energy
?U Q - W

• Isovolumetric Process no change in Volume and
  therefore no Work done, so ?U Q
• Isothermal Process no change in Temperature and
  internal energy, so Q W
• Adiabatic Process no energy transferred as
  heat, so Q0, so ?U -W
• Isolated system no heat or work interaction, so
  UiUf

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A heat engine

• Transforms heat at high temperature into
  mechanical energy and low-temperature waste heat
• A heat pump (refrigerator) absorbs heat from the
  cold reservoir and gives off heat to the hot
  reservoir.

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2nd Law of Thermodynamics

• In the 19th Century French engineer Sadi Carnot
  studied the ability of engines to convert thermal
  energy into mechanical energy.
• He developed a logical proof that even an ideal
  engine would generate some waste heat.
• Carnots result is best described by the term
  entropy which is the measure of the disorder in a
  system.

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• The change is entropy, ? S, is shown by the
  equation
• S Q / T Units J/K
• The change in entropy of an object is equal to
  the heat added to the object divided by the
  temperature of the object.
• Natural processes occur in a direction that
  increases the entropy of the universe. All
  processes tend toward disorder unless some action
  occurs to keep them ordered. i.e., heat can flow
  only from hot to cold naturally.

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Practice Problems
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12/32 answer
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