Welcome to Physical Chemistry II - Physical Chemistry II

In this second course of the Physical Chemistry sequence at WashU, we shift from the microscopic perspective you explored previously to the macroscopic framework that governs the behavior of chemical systems. While Physical Chemistry I focused on the quantum-mechanical underpinnings of atomic and molecular properties, this course emphasizes the thermodynamic laws and principles that emerged well before we had a clear microscopic picture—yet continue to hold true even in light of our modern understanding.

Long before quantum mechanics sharpened our knowledge of atoms and molecules, a series of remarkably robust laws described how matter behaves on larger scales. These thermodynamic principles remain so powerful that, as Einstein famously remarked:

[Thermodynamics] is the only physical theory of universal content concerning which I am convinced that, within the framework of the applicability of its basic concepts, it will never be overthrown (for the special attention of those who are skeptics on principle).
Einstein, A.; Schilpp, P. A., Ed. Autobiographical Notes. Centennial ed.; Open Court: La Salle, IL, 1979; pp 1–89. ISBN 0875483526. Permalink

In this course, we will develop the laws of thermodynamics and statistical mechanics—the framework that deepens our microscopic understanding and connects quantum theory to macroscopic observations. I like to refer to this course as “Statistical Thermochemistry” because it bridges the inherently quantum nature of particles with the bulk properties they collectively produce.

Here are a few key themes to keep in mind this semester:

Statistical Mechanics as a Bridge: Statistical mechanics connects the quantum-level description of matter to the large-scale thermodynamic properties we measure. By applying statistical methods to quantum states, we can predict macroscopic observables such as heat capacities, entropies, and free energies.
Spontaneity Through Competition: Chemical spontaneity arises from the interplay between the strength of chemical interactions (encapsulated by enthalpy) and the distribution of states available to a system (encapsulated by entropy). Understanding how these two factors compete is central to predicting whether processes will occur without external influence.
Beyond Equilibrium: While the equilibrium perspective provides a foundational understanding, it captures only part of the story. Real systems often evolve over time, influenced by non-equilibrium dynamics and kinetics. Although this course focuses on statistical thermodynamics, a complete picture of chemical behavior ultimately includes these time-dependent processes, which you will explore later in Chem 403.

By the end of this course, you will gain a deeper appreciation for how thermodynamics and statistical mechanics provide a unified framework for interpreting the chemical world—one that remains as relevant today as it was more than a century ago.