Kinetics

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Kinetics

• Chapter 19 part 3

2
a Review

• The entropy of a substance changes with its state
  of matter.
• S solidltS liquid ltltltS gas

3
Spontaneous reactions

• Burning paper?
• Yes
• Rusting nail?
• Yes
• Break down of water into O2 and H2.
• No
• Graphite into diamond?
• No

4
Gibbs Free Energy

• The sign, /- of the change in Free Energy, ?G,
  tells us if a reaction is spontaneous or not.

5

• If ?H is exothermic ?S is random
• Then ?G is negative the rxn is spontaneous.
• If ?H is endothermic ?S is ordered
• Then ?G is positive the rxn is not spontaneous.
• If ?H is exothermic ?S is ordered
• Then it depends on T
• If ?H is endothermic ?S is random
• Then it depends on T

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• - - -()
• -(-)
• /- -()
• /- - -(-)

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Mechanisms

• Show the Catalyst and the Transition state

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Catalyst

• A catalyst speeds up a reaction without being
  explicit in the overall balanced equation.
• It does this by providing an alternate mechanism
  for the reaction that has a lower activation
  barrier than does the uncatalyzed pathway.

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Transition state

• It is defined as the state corresponding to the
  highest energy along this reaction coordinate.
  From this point it will always go on to form
  products .

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Mechanism
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Mechanism

• 1. XY C ? 2. XCY
• 3. XCY ? 4. XYC
• The summation is
• XY ? X Y
• The catalyst is found in 1 4
• The transitional state is found in 2 3