CH302H - Principles of Chemistry II: Honors
Spring 2016, Unique 49420

Lecture Summary, 28 January 2016


Molar entropy (or 3rd law entropies):  Today we looked at patterns for the magnitude of molar entropy for similar compounds at the standard state.  We made a few conclusions:

  1) Molar entropy increases with FW
  2) Molar entropy increases with additional phase transformations.
  3) Molar entropy increases with conformational degrees of freedom from molecular structure.

We also saw that Hess' law can be applied to determining changes in entropy from a chemical reaction by tabulating all of the contributions to molar entropy from reactants and products. 

Free energy: We discussed the problem of having to calculate the entropy of the universe in order to know the direction of spontaneous change.  To get around this problem, we defined a new state function, called "free" or "available" energy (G), which combines a systems change in internal energy and change in entropy to understand if that system will change spontaneously.