CH302H - Principles of Chemistry II: Honors
Spring 2014, Unique 51880

Lecture Summary, 4 February  2014

Entropy as disorder:  We worked through a thought experiment in which we defined a property called "microstates."  Microstates (W) are experimentally indistinguishable configurations that all give the same experimentally distinguishable result.  Boltzmann quantified the entropy of a system based on the number of available microstates:

   S = kb ln W

A system will move spontaneously in the direction of increasing number of microstates:

  deltaS = kb ln(Wf/Wi) > 0

This defines both the direction of entropy and provides a molecular level reason for quantifying the magnitude of change in entropy.  This also implies entropy is a state function, because the function is defined only by the number of microstates, which is a property of a system that is independent of how it acquired those microstates.

Entropy as heat:  We also defined entropy in terms of the heat released by a system that is not available to do work.  When this heat is divided by T, the result is a state function.

      deltaS = q/T.

We developed a series of expressions to define changes in entropy at constant temperature, constant volume, and constant pressure.  We also worked through a very famous proof that entropy is a state function, the Carnot cycle.