Energy

1
Energy Chemical Change

• Chapter 16.5 Notes
• Reaction Spontaneity

2
Spontaneous Processes

• Physical/chemical change that occurs with no
  outside intervention
• Energy must sometimes be applied to initiate
• eg lighting a bunsen burner
• ?H neg. ? exothermic ? spontaneous
• ?H pos. ? endothermic ? non-spontaneous

3
Entropy

• Entropy measure of the disorder/randomness of a
  system
• Molecules are more likely to exist in high state
  of disorder (mixed up) than a low state of
  disorder (organized) p. 514
• Law of disorder spontaneous processes always
  proceed in such a way that the entropy of the
  universe increases

4
Changes in Entropy (?S)

• ?S Sproducts Sreactants
• Entropy changes w/ changes in state
• s ? l, entropy increases ?Ssystem gt 0 ()
• l ? g, entropy increases ?Ssystem gt 0 ()
• Dissolving gas in a solvent, entropy decreases,
  ?Ssystem lt 0 ()
• Dissolving solid/liquid in solvent, entropy
  increases, ?Ssystem gt 0 ()
• Assuming no changes in physical state, if there
  are more gaseous products than gaseous reactants,
  entropy increases, ?Ssystem gt 0 ()
• Increase temp., entropy increases, ?Ssystem gt 0
  ()

5
Entropy, the Universe, Free Energy

• For any spontaneous reaction, ?Ssystem gt 0.
• ?Suniverse ?Ssystem ?Ssurroundings
• For an exothermic process, ?Hsystem is and
  ?Ssurrounding is (?Suniverse is ).
• If entropy increases, ?Ssystem is
• Free Energy energy available to do work (G)
  useful energy
• ?G () spontaneous
• ?G () nonspontaneous
• ?Gsystem ?Hsystem T?Ssystem