IMT Chapter 7 Entropy and the Second Law

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IMT Chapter 7 Entropy and the Second Law

• The Big Picture
• Entropy
• Second Law of Thermodynamics
• Measuring and Calculating Entropy

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I. The Big Picture (where weve been and where
were going)

• Theme How can we predict the position of
  equilibrium? or What makes a reaction occur?
• The equilibrium state is the most probable state.
• The most probable state is determined by
  competition between energy levels.
• Competition
• Lo T lower lying levels favored
• Internal Energy (U)
• Hi T more closely spaced levels are favored
• Entropy (S)

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II. Entropy

• First described by Clausius (1865)
• Boltzmanns second great achievement (1869)

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III. Second Law of Thermodynamics

• Clausius (1865)
• The total entropy of the universe is always
  increasing.
• How do we tie in Boltzmann?
• But what about ?S q/T ?

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IV. Measuring and Calculating Entropy

• Measuring S can use Clausius relation
• Third Law of Thermodynamics (Boltzmann)
• The entropy of a perfect crystal at 0 K is
  zero.
• How do we measuring absolute entropy?
• Standard Molar Entropy (Sº)
• absolute entropy of 1 mol of a substance at 1 bar
  pressure
• Sº298 absolute entropy of 1 mol of a substance
  at 1 bar pressure and 298 K (Table 7.1 and
  Appendix IV)

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Points about Sº298

• solids lt liquids lt gases
• heavier gases have larger S than lighter gases
• noble gases have very low S
• Diamond has the lowest S

How do we calculate entropy changes for a
reaction?