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

Lecture Summary, 6 February  2014

Entropy continued:  We worked through a number of examples of determining change in entropy of a system undergoing change at constant volume, temperature, and pressure.  We examined the particular case of entropy change of vaporization to explain a curious observation; many different molecules with a wide variety of sizes, shapes, and chemical functionalities, have nearly identical deltaS(vap) (often called Trouton's Law).  In all cases we were careful to evaluate our answers based both on whether the results of the equation made sense AND for molecular reasons based on the number of microstates. 

Third law of thermodynamics:  Finally, we stated the third law of thermodynamics, which states that the entropy of a pure crystalline solid at 0 K is 0.  This will allow us to define a so-called "molar entropy" of any atom or molecule at a standard state.