- 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
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.