Welcome to Physical Chemistry II#
In this second course of the Physical Chemistry sequence at WashU, we move from the microscopic perspective you explored previously to the macroscopic framework that governs the behavior of real-world chemical systems. While Physical Chemistry I focused on the quantum mechanical underpinnings of atomic and molecular properties, this course will emphasize 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 crystallized our knowledge of atoms and molecules, a series of remarkably robust laws described how matter behaves on a larger scale. These thermodynamic principles remain so powerful that, as a famous physicist once 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 explore the laws of thermodynamics and introduce you to the world of statistical mechanics—a field that not only deepened our microscopic understanding but also helped unify quantum theory with our macroscopic observations. I like to refer to this course as “Statistical Thermochemistry” because it bridges the gap between the inherently quantum nature of particles and 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 phenomena like 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 the time-dependent processes 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.
Module 1. Equations of State