• Thermodynamics let us predict whether a process will occur but does not tell us about the amount of time required
  • A spontaneous or “thermodynamically favored” process is one that occurs without intervention; the reaction rate may be fast or slow

○ Ex: a ball rolls down a hill but never spontaneously rolls back up


  • Entropy (S): measure of the randomness/disorder of a system

             ○ More disorder = greater entropy

  • Trends in entropy:

             ○ Ssolid < Sliquid << Sgas

             ○ Molecules that are more more complex, have weaker InterMFs, and greater molar mass have higher entropy

Sign of ΔS ΔS = + ΔS = –
Meaning Things are becoming more disordered = thermodynamically favored Things are becoming more organized = unfavored
Example Decomposition reaction (one reactant becoming two products)Dissolving Endothermic reactionsProducts have more moles of gas Increase volume → greater dispersion of molecules Molecules have greater distribution of energy Synthesis reactions (two reactants become one product)Exothermic reactionsProducts have less moles of gas Decrease volume → particles are less dispersed

Second Law of Thermodynamics

  • In any thermodynamically favored process (energy transfer or transformation), there is usually an increase in the entropy of the universe
  • Since energy never flows spontaneously in the other direction, the entropy of the universe is always increasing
  • usually a favored process 
  • usually NOT a favored process (favored in the opposite direction)