- 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
- 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) 